What is the main reason why mercury is in our water?...?

Question

....and what can we do to save the organisms that are tainted with it, if anything?

Answer 1

Mercury is very heavy and doesn't mix with the water.

Answer 2

It comes from burning fossil fuels, which have mercury in them.

Once it's in an organism nothing can be done.  And taking it out of the water is too expensive.  Like most environmental pollution, it's way easier to stop it at the source than to clean it up after it's released.

Answer 3

The main source of mercury is from burning coal. When the coal is burned to make electricity, mercury (Hg) is also given off and goes into the atmosphere. it hen ends up in the rain clouds and falls to earth, entering the oceans, lakes , rivers all over the globe.

Another source of Hg is from gold mining. Hg was used to extract gold for centuries. This is the source of much of the Hg pollution in San Francisco and the Amazon.

San Francisco, CA area is also a location for mercury mining.

There isn't much we can do about the Hg that is already in the system. Hg is the only biotoxin that bioaccumulate at every step of the food chain. that means, algae pick it up, the algae are eaten by small fish that concentrate the mercury, the small fish are eaten by bigger fish and so on, until we eat the fish.

Mercury is pretty stable and has a long half life. I am afraid we are stuck with it for a while. The best thing to do is stop adding it to the system.