Algae are simply aquatic plants that lack a vascular system and thus obtain their nutrients directly from the water as opposed to the soil. Algae can live in freshwater or salty water. Some algae are microscopic and others are large. Common examples include pond scum, kelp, and red tides. Algae are critical to life on earth as they form the basis for many food chains and they produce oxygen. Because algae are so abundant on Earth, much of the oxygen in our atmosphere comes from algae. One fun example of beneficial algae is the commercial food industry that sells algae in the form of drinks or powders. Algae also create habitat for animals ranging from freshwater fish (e.g. mats of rooted algae in rivers) to otters (e.g. kelp forests in the ocean). Algae in and of themselves are good guys, its just that excessive amounts can create problems either by depleting oxygen while they decompose or by the neurotoxins that are harmful to humans and animals that some algae produce. One more fun fact is that if we ever get to the point of terra forming another planet, we will need to introduce algae to create the oxygen atmosphere.

Algae are:
1. The base of the food chain in almost all aquatic ecosystems: everything living in the water either eats algae or eats something that eats algae.
2. Most of the Earth's oxygen is produced by algae.
3. Algae produce the structure of a number of aquatic ecosystems (e.g. kelp forests).
4. Algae maintain the chemical balance of the atmosphere by precipitating a number of gasses, carbon dioxide in particular, and turning it into stone.

In short, life as we know it would not exist without