River water ecosystems support a wide range of animals, microbes and plants that differ from other terrestrial and seawater based systems. Animals living in river environments survive due to the abundance of these plants. Plants are found in the river water and near the river water in the riparian zone. Plants on the riverbank drop leaves into the river water creating food for fish like crayfish.
Macrophytes are large, leafy plants found in river streams and also wetlands and lakes. Macrophytes can be grouped into four categories that describe how they grow. These include floating unattached, floating attached, submersed and emergent. Floating unattached plants float at or near the water surface with any roots hanging free in the water. Floating attached plants have roots anchored below the water surface and leaves floating near the top. Submersed plants live entirely under the water surface while emergent plants' roots grow underwater but stems and leaves grow above the water. Some examples of river water macrophytes include lilies, duckweed, tape grass or eel grass and hyacinths.
Algae and Diatoms
Different types of algae thrive underwater in river systems. Their chlorophyll allows them to photosynthesise. Algae blooms can occur naturally or become toxic. Blue-green algae can arise in rivers due to warmer weather conditions, low water flow and the lack of water flow. Besides algae, river water plants include brownish-yellow plants called diatoms. Diatoms are unicellular organisms with a yellow-brown chloroplast that enables them to photosynthesise. River herbivores feed on diatoms. Both algae and diatoms cover macrophytes and feeding opportunities for river herbivores.
Water Cress and Water Moss
Water cress is a hardy herb found in or around water. It can be used as salad greens or for garnish. It can be eaten raw. Watercress used to be used as a domestic remedy for the illness scurvy. Water moss is dark green and lives underwater in rivers where it attaches to stationary objects like rocks or logs. Water moss has sharply pointed, ridged, overlapping leaves and does not produce flowers.