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Matthew Haughey wrote an interesting article on his blog about evaporation beds on Google Maps

The article was about Dead Horse Point State Park in Utah (pictured left), which shows a series of strongly covered pools. The author suggests that the pools are runoff pools to clean water used in agriculture or mining. Feedback from locals confirms that the pools are used by the local mining industry. By running the wastewater through pools in a hot, windy valley, the evaporation (which is increased in this environment) causes metals and pollutants such as lead to drop out of solution, preventing it from entering the local water table where it can posion flaura and fauna. The minerals may also contain Potash, and so could be sold as fertiliser. You can also see these pools to the left of this photo of nearby Hurrah Pass.

Another Google Maps page showing an area of San Franciso Bay shows a similar image. Here, water used to irrigate agricultural land is passed through pools containing algae, which consume the chemicals in the water. As the chemicals are consumed by the algae, different species bloom (dependant on which chemicals are present), producing the strong colours seen. If the water were allowed to flow into the bay, the blooming algae would cause oxygen starvation in the water, destroying the native fish and plants.