Plants and algae are important to the freshwater ecosystem. They provide food and shelter to organisms that live in it to ether hide or shade from the sun and predators like bigger fish,crocs E.T.C. Some plants have adapted to there ecosystems like fast moving rivers and streams some adapt by changing there growth structures to prevent from being carried away so they flow with it. Plant that live in still waters have adapted differently like water lilies,algae and duckweed float on the surface of the water, cattails and weed like plants grow on the freshwaters shoreline.
Animals on land also take advantage of the freshwater in it they can drink it, bath in it and many other things. It's not just the marine animals that can take advantage of the freshness of the water.