Aquatic plants are perhaps the most powerful water filter that nature has to balance the chemistry of lakes, rivers and oceans.
Caulerpa is one family grouping of complex forms of saltwater plants
referred to as macroalgae. Microalgae or phytoplankton are single celled plants.
In the ocean sponges play a similar role not to mention the mega-trillions of aerobic and anerobic bacteria
that also play a role in filtering fresh and salt water.