What’s the difference between freshwater, saltwater, and brackish water? 

Freshwater is water, without salt or other minerals, that occurs naturally, such as in rivers, streams, ice caps, glaciers, bogs, ponds, and groundwater.

Saltwater is sea water that occurs in the ocean and in marine environments, such as salt lakes, salt pans, and brine pools. It is salty. It has a high salinity level.

Brackish water occurs in areas where the seawater from the ocean meets the freshwater from a river, such as in estuaries. An estuary is on the coast, where a river meets the sea. It is a transition zone.