Eutrophication is the over growth of algae in water ecosystems where nutrients are usually limiting. Many fresh water systems are ‘oligotrophic’, meaning that the growth of primary producers (algae) is limited not by dissolved gas or light, but by nutrients such as nitrates and minerals. The organisms in these environments have evolved to be optimally suited to these conditions, and everything works fairly well. But when someone builds something next to a lake (e.g. golf course), and the fertilizer being used on the grass runs off into the lake, the algae grows too fast for the rest of the ecosystem to keep up, and overgrows the lake, killing everything in it. That’s one example, there are many otherThe solutions generally involve not washing lots of nutrients into lakes and streams (or the ocean, which, although generally full of nutrients, can also be locally overwhelmed with runoff, especially in coral reef environments).