That's a mystery - why is the water in the sea salty, but not in rivers and lakes? There is currently no single correct answer to this question, and there are active debates and discussions on this matter in the scientific world.
Scientists only identify two main theories, each of which seems to be correct, but at the same time they contradict each other, and there are several compelling arguments against each.
First theory. The seas and oceans acquired salinity as a result of slow and gradual processes.
So, according to this theory, sea water became salty as a result of the water cycle in nature. This process can be described in more detail as follows: rain gradually washed away and dissolved mineral salts contained in rocks and soils, and rainwater flowed into rivers. Rivers also wash particles of various salts from the bottom, which then fall into the seas and oceans under the influence of the current. Under the influence of the sun's heat, the water over the seas evaporated and fell back to the ground in the form of rain and other precipitation - the process was repeated. And salt, of course, accumulated in the oceans over millions of years, gradually increasing the level of salinity. But here a big question arises: Why has the salinity level of ocean water not increased for more than 500 million years and remained at the same level of 35 ppm (35 grams of salt per 1 liter of water), while the rivers have not stopped supplying mineral elements all this time?
Second theory. Ocean water was salty from the very beginning.
At the initial stages of the formation of our planet, volcanic smoke was emitted from the depths of the mantle along with the first water vapor into the atmosphere. These smokes were enriched with waste products of volcanoes - chlorine, phosphorus and bromine. Water mixing with these vapors looked more like acid than water. Primary acidic water filled the future oceans and seas and destroyed the crystalline rocks of the earth's crust at the bottom, as a result, elements such as potassium, calcium, magnesium, sodium were released... Next, a simple chemical reaction occurred in which chlorine interacted with sodium, and, in fact, it turned out to be salt. Over time, volcanic activity decreased and water salinity levels stabilized.
Both theories do not give an exact answer, but only suggest the possible course of events and processes. We have yet to find out the true reason for this interesting question.
As you know, sea water is a solution of various salts, giving it a characteristic bitter-salty taste.
At the same time, rivers that flow into seas and oceans consist only of fresh water, the concentration of dissolved salts in which is significantly lower than in sea water. But how can this be, why do sea and river water contain such different amounts of dissolved substances? Let's find out what scientists think about this.
Version No. 1 – salt accumulated gradually
Rain or melt water is an almost pure distillate: it contains a minimal amount of substances collected during the fall in the atmosphere to the surface of the earth.
Absorbing into the soil and collecting in streams and then in rivers, water dissolves minerals, which are then carried with river water into the ocean. Evaporation from the surface of the ocean, which occurs much more intensely than on land, again raises clean, distilled water into the atmosphere, and salts remain in the ocean.
This process continues for billions of years, during which the concentration of salts in sea water has increased tenfold. This hypothesis is supported by the existence of salt lakes on the land surface that have never been in contact with the waters of the World Ocean. As a rule, these are closed reservoirs into which water only flows in the form of streams, but does not flow out. 
True, this theory does not explain the difference between the composition of salts in sea and river water. Fresh water also contains various salts, but these are, as a rule, carbonates - salts of carbonic acid, which are formed as a result of the breakdown of organic residues - fallen leaves, etc.
Sea water contains up to 80 different chemical elements and their compounds, but the predominant substance in it is sodium chloride, or ordinary table salt, which gives a characteristic salty taste. Where does table salt come from in the sea if it is not washed off the land? This question is answered by the second version proposed by scientists.
Version No. 2 – salt was in the water initially
Billions of years ago, when our planet was still very young, violent volcanic activity took place in its crust. Eruptions large and small were a daily occurrence.
A large amount of volcanic gases, which contained chlorine, bromine and fluorine in free form, were released into the atmosphere and waters of the World Ocean. The atoms of these elements reacted with water vapor and formed acid molecules, so in the initial period of its existence, sea water was not salty, but acidic. 
These acids, having high chemical activity, reacted with metals contained in volcanic rocks - sodium, magnesium, potassium, etc. The compounds formed as a result of the reaction were the salts that gave the water its today’s “sea” taste.
The acids were almost completely neutralized, and the modern composition of sea water stabilized about 500 million years ago - a fact proven by studying the rocks of the sea and ocean floor.
How did it all really happen?
Most likely, both processes described above are to blame for the fact that sea water has become salty. The water of the World Ocean actually received its initial level of salts due to the active volcanic activity of the earth’s crust.
Today's salt levels are maintained by the leaching of minerals by rivers, as well as by the activity of numerous living organisms that use dissolved substances to build their cells.
Interesting fact: although sea water is completely undrinkable, the concentration of salt in it corresponds to the salt content in human blood plasma. 
Daily bathing in sea water strengthens the body and helps fight many different diseases of the skin, respiratory tract, nervous system, etc.
Why is the water in the sea salty? There is so much water on the Earth's surface that it is often called the "blue planet." Land occupies only 29% of the Earth's area, and the remaining 70% falls on the mysterious and almost unexplored oceans. Obviously, such a quantity of water cannot have an absolutely identical composition, as can be seen from the example of the different saturation of salts in rivers and seas. But how to explain these differences?
Water is famous for its ability to erode any type of rock. It doesn’t matter what sharpens the stone - a powerful stream or a separate drop - the result is always predictable. During the destruction of the rock, it removes easily soluble components from it. Salts, which are also leached from the stone, give the water its characteristic taste.
Scientists have not been able to come to a consensus as to why some bodies of water have fresh water and others have salt water. To date, two complementary theories have been formulated.
First theory
The first theory is based on the fact that fresh water is just as salty as sea water, but the concentration of salt in it is seventy times lower. Salt-free water can only be obtained in laboratory conditions by distillation, while natural liquids have never been and will not be purified from chemical components and microorganisms.
All impurities that dissolve and are then washed away by water from rivers and streams inevitably end up in the waters of the World Ocean. Then the water evaporates from its surface and turns into, and the salt becomes part of its chemical composition. This cycle has been continuously repeated for two billion years, so it is not surprising that during this time the World Ocean has become so rich in salts.
Proponents of this theory cite salt lakes that have no drainage as evidence. If the water did not initially contain a sufficient amount of sodium chloride, they would be fresh.
Sea water has one unique property: it contains almost all existing chemical elements, including magnesium, calcium, sulfur, nickel, bromine, uranium, gold and silver. Their total number is close to sixty. However, the highest level is due to sodium chloride, also known as table salt, which is responsible for the taste of sea water.
And it was the chemical composition of water that became the stumbling block to this hypothesis. According to research, sea water contains a high percentage of hydrochloric acid salts, while river water contains carbonic acid salts. The question of the reason for such differences still remains open.
Second theory
The second point of view is based on the assumption of the volcanic nature of ocean salts. Scientists believe that the process of formation of the earth's crust was accompanied by increased volcanic activity, as a result of which gases saturated with fluorine, boron and chlorine vapors were transformed into acid rain. From this we can conclude that the first seas on Earth contained a huge percentage of acid.
Under such conditions, living organisms could not originate, but subsequently the acidity of ocean water decreased significantly, and it happened like this: acidic water washed out alkalis from basalt or granite, which were then transformed into salts that neutralized ocean water.
Over time, volcanic activity weakened significantly, and the atmosphere began to gradually clear itself of gases. The composition of sea water also stopped changing and reached a stable state five hundred million years ago.
However, even today the salinity of the water is controlled by a large number of underwater volcanoes. When they begin to erupt, the minerals in the lava mix with the water, raising the overall salt level. But, despite the fact that a new portion of various salts enters the World Ocean every day, its own salinity remains unchanged.
Returning to the question of carbonates disappearing from fresh water when it enters the sea, it is worth adding that these chemicals are actively used by marine organisms to form shells and skeletons.
Everyone knows that sea water is very harmful and tastes unpleasant. However, many adhere to the erroneous ideas that it can easily replace fresh water in conditions of extreme necessity. Such misconceptions can not only harm a person who finds himself in an extreme situation, but also cost him his life.
The thing is that the load associated with filtering any liquid entering the body falls entirely on the kidneys. Their task is to remove excess fluid through urine and sweat. In the case of sea water, the kidneys will have to process a large amount of salts, which can be retained, forming stones and impairing the functioning of the entire body.
Thanks to the kidneys, during the day a person excretes about fifty percent of the liquid he drinks during this period. Instead, excess sodium, calcium and potassium salts leave the body with urine. Sea water is so saturated with salt that the kidneys wear out very quickly, trying to cope with the work that is too much for them. One liter of sea water contains thirty-five grams of salt, which is several times higher than its content in human water.
The daily norm of liquid an adult drinks includes not only water, but also moisture received during meals. Every day, from fifteen to thirty-five grams of salt deposits in the body, which the kidneys successfully remove.
Thus, it turns out that in order to get rid of thirty-five grams of salt that entered the body along with a liter of sea water, it will have to produce one and a half liters of its own fluid, taking into account the fact that the amount of water drunk will clearly not be enough for this. To fulfill their task, the kidneys will begin to work to the limit of their capabilities and very quickly fail.
In addition, a lack of fluid coupled with a critical level of salt in the body will lead to severe dehydration, and after a few days the kidneys will stop functioning. Excess salt will cause damage to internal organs, the first of which will be the kidneys and gastrointestinal tract. Due to a lack of moisture, irreversible changes will also occur in the nervous system.
In addition, dehydration in the process of quenching thirst with sea water is caused by the presence of magnesium sulfate in its composition, which has a laxative effect. As a result, dehydration occurs much more rapidly than usual, and the person quickly loses strength and ability to fight for survival.
The body can no longer produce its own fluid and cope with high salt levels. In addition, sea water contains other dangerous substances, on the absorption of which the body will spend its last resources.
However, it is still possible to survive in the absence of fresh water. Some scientists and survival experts advise squeezing the liquid out of fish, no matter how strange it may sound. There are several documented cases where people managed to escape with the help of such fish “juice”.
Thus, the salt contained in the waters of the World Ocean can bring people both the sensation of flight from swaying on the surface of the sea, and become their worst enemy, gradually depriving them of the ocean that is contained in the body of each of us.
Why is the water in the sea salty and not fresh? There are several theories about this. Some researchers claim that the salt remains from water from flowing rivers, others that it enters the water from rocks and stones, and others believe that the reason is volcanic emissions. In addition to salt, sea water contains many different substances and minerals.
Why is there salty water in the sea?
The seas are much larger than the rivers, but their composition remains virtually unchanged. If all the sea salt were spread on land, we would get a layer more than 150 meters thick, which is equal to the height of a 45-story building. Let's consider several theories why the sea is salty:
- The seas become salty from the water of the rivers flowing into them. This is not surprising. River water seems quite fresh, but it also contains salt. Its content is 70 times less than in the waters of the World Ocean. Flowing into the sea, rivers dilute their composition, but when river water evaporates, salt remains at the bottom of the seas. This process took place over billions of years, so the salt accumulated gradually.
- The second theory is why there is salty water in the sea. Salts that flow from rivers into the sea settle at the bottom. Over the course of many years, huge blocks of stone and rocks are formed from salts. Over time, sea currents wash away easily soluble substances and salts from them. Particles washed out of rocks and rocks make seawater salty and bitter.
- Another theory suggests that underwater volcanoes can release a lot of substances and salt into the environment. When the earth's crust was formed, volcanoes were extremely active and released acidic substances into the atmosphere. The acids formed rain and formed seas. At first they were acidic, but then the alkaline elements in the soil reacted with the acids and the result was salt. Thus, the water in the seas became salty.
Other researchers associate the salinity of sea waters with winds that bring salts into the water. With soils through which fresh liquid passes and becomes enriched with salts, and then flows into the ocean. Sea water can be saturated with salt by salt-forming minerals that make up the ocean floor, which get there from hydrothermal sources.
Why is the water in the seas constantly salty and this composition does not change? Sea water is diluted by rain and inflowing rivers, but this does not make it any less salty. The fact is that many of the elements that make up sea salt are absorbed by living organisms. Coral polyps, crustaceans and molluscs absorb calcium from salt, as they need it to build shells and skeletons. Diatom algae absorb silicon dioxide. Microorganisms and other bacteria consume dissolved organic matter. After organisms die or are consumed by other animals, the minerals and salts in their bodies return to the seafloor as remains or decay debris.
Sea water can be salty and varies depending on the time of year as well as climate. The highest salinity levels are found in the Red Sea and the Persian Gulf, as they are hot and evaporate intensely. In sea waters, which receive a lot of precipitation and a large volume of fresh water from large rivers, the salinity is much lower. The least salty seas and oceans are near polar ice, as they melt and dilute the sea with fresh water. But while the sea is covered with a crust of ice, the level of salt in the water rises. But in general, the salt levels in seawater remain constant.
The saltiest seas
The first place in salinity is occupied by the unique Red Sea. There are several reasons why this sea is so salty. Due to its location above the sea surface, there is low precipitation and much more water evaporates. Rivers do not flow into this sea; it is replenished thanks to precipitation and the waters of the Gulf of Aden, which also contain a lot of salt. The water in the Red Sea is constantly mixing. Evaporation occurs in the upper layer of water, and salts sink to the seabed. Therefore, the salt content increases significantly. Amazing hot springs were discovered in this reservoir; the temperature in them is maintained from 30 to 60 degrees. The composition of the water in these sources is unchanged.
Due to the absence of rivers flowing into the Red Sea, dirt and clay do not fall into the Red Sea, so the water here is clean and clear. The water temperature is 20-25 degrees all year round. Thanks to this, unique and rare species of marine animals live in the reservoir. Some consider the Dead Sea to be the saltiest. Indeed, its water contains a large amount of salt, which is why fish cannot live in it. But this body of water does not have access to the ocean, so it cannot be called a sea. It would be more correct to consider it a lake.
Almost each of us, having carelessly opened our mouths while swimming in the sea and taken a sip of water, wondered, why is it salty? Of course, you can be like the ancient Greeks, who believe that the waters of the seas and oceans are the tears of Poseidon. But now they don’t believe in fairy tales, and a strictly scientific substantiation of the reasons for the appearance of salt in sea waters is required.
Theories of sea salinity
Researchers on this long-standing problem fall into two camps, proposing specific theories.
The salinity of the seas gradually increased
This was facilitated by the natural water cycle. Precipitation, acting on the rocks, washed out minerals from it, which ended up in river systems. And from the rivers, water saturated with salts was already flowing into the seas. The river flows themselves also contributed to the leaching of salts from soils and rocks.
Then the tireless Sun began to work. Under its hot influence, water evaporated, no longer containing salts. Distilled moisture also precipitated on the surface of the planet and continued its work of saturating the seas with salts.
The process continued for many millions of years, salt accumulated in sea waters, acquiring exactly the consistency that we now observe. Everything is simple and quite logical. However, there is some inconsistency in this theory.
For some reason Over the past half a billion years, the concentration of salts in sea waters has not changed. But rainfall and rivers are as active as ever. This discrepancy can be explained as follows. Salts delivered by rivers to the subsoil of the sea do not dissolve in them, but settle on the bottom surfaces. From them various rocks and rocky formations are formed.
Sea waters have been salty from the very beginning
During the formation of the earth's crust, powerful volcanic activity was observed. Thousands of volcanoes emitted gigantic amounts of all kinds of substances into the atmosphere, among which were:
- chlorine;
- bromine;
- fluorine.
Acid rains constantly fell on the earth's surface, contributing to the birth of seas.
Their oxidized waters interacted with rocks and pulled out from them:
- potassium;
- sodium;
- magnesium;
- calcium.
As a result, salts were obtained, with which the waters were saturated. But 500 million years ago this process ended.
More interesting versions of salt formation in the seas
The search for versions of the appearance of salty and fresh waters does not stop. At this time, two are the most interesting.
- Our planet was formed exactly in this form - salty seas and fresh rivers. If it were not for river currents, the rivers could also become salty, but fortunately, the seas cannot flow into them.
- Animals contributed. For a long time, the waters were salty everywhere. But animals very actively consumed it from rivers and lakes in order to obtain the necessary chemical elements for the development of their organisms. Over many hundreds of millions of years, the rivers have lost all their sodium chloride reserves. But this version is more entertaining.
Features of sea water
For people, fresh water is familiar and its beneficial properties are obvious. But sea waters also have their own characteristics.
- It is absolutely not suitable for drinking. The content of salts and other minerals in it is very high. They can only be removed from the body with more water. But if such water is desalinated, then it is quite drinkable.
- In some countries, sea salt water is used for domestic needs. For example, in drainage sewer systems.
- The benefits of sea water for treatment have long been known. It is used in the form of baths, rinses, and inhalations. This helps fight respiratory diseases and relieves muscle tension. Water with a high salt content also exhibits antibacterial properties.
The salinity of the waters of some known seas is as follows (at 0/00):
- Mediterranean – 39;
- Black – 18;
- Karskoe – 10;
- Barentsevo – 35;
- Red – 43;
- Caribbean - 35.
Such a disproportionate salt content in the waters of different seas is influenced by specific factors:
- drainage of rivers and streams flowing into them;
- precipitation water;
- transformation of sea ice;
- vital activity of all kinds of marine organisms;
- plant photosynthesis;
- bacteriological activity.
Now you know why the sea is salty!
