the answer is phytoplankton or plankton
plankton
Acquaculture
Organisms that are permanently attached to a surface, instead of being able to move freely, are called sessile. Plants, mussels and barnacles are examples of sessile organisms.
Phytoplankton
A large stream of surface water is usually called a river. A river is freshwater and runs from high to low ground.
Phytoplankton
A freshwater mussel is also called a unionid mussel or naiad.
Freshwater protists with two flagella that can be photosynthetic or heterotrophic are called euglenoids. They are single-celled organisms that can switch between autotrophic and heterotrophic modes of nutrition depending on environmental conditions.
ground water
Saltwater and Freshwater mixed is called brackish water.
Large streams of surface water are called rivers. Rivers flow downstream towards larger bodies of water, such as lakes or oceans, and play a key role in shaping the landscape and supporting ecosystems.
An estuary is the place where freshwater and saltwater meet.