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Water Questions & Answers
Why are some lakes full of algae?


First of all, plants naturally grow in and around lakes. Maybe you're asking about a lake that is being choked off by too much algae. In many cases, humans are responsible because these lakes are being fed too much food! There are certain chemicals we use that are nutrients (food) to plants. At home, we fertilize our yards with nitrogen, potassium, and phosphorus. These chemicals wash off lawns and eventually get into the water system, such as into creeks, rivers, and lakes. Once there, algae and plants have a feast on this "food." Things used to be worse for many water bodies; phosphorus used to be an ingredient in laundry detergents, but this has generally been phased out.

Algal blooms come and go .... luckily

Algal blooms are true to their name, though ... they bloom for relatively short times. But just because they are less than permanent fixtures in the hydrologic landscape doesn't mean that they can't have a big, and nasty, impact on a poor lake subjected to them. The left-side picture below show Brookmill Park Lake, a pleasant country lake in a public park near Greenwich in Great Britain. Water in the lake comes from streamflow from a nearby stream. Certainly a pleasant pastoral setting for any person or duck.

The right-side picture below shows Brookmill Park Lake again, 11 months later in September 2009. A number of things, stagnant water movement, high temperatures, and/or an influx of nutrient material, such as lawn fertilizers, could have contributed to the explosive growth of algae to form this thick green mat. I'm not sure if odor was a problem at this time, but I'm sure even if no smells were present, the local residents did not sit by this lake for a picnic. Well, at least the duck seems to be enjoying having this lake all to himself, unless he is stuck in the gooey mess and can't get out.

Brookmill Park Lake, Deptford, Lewisham, Great Britain. Left picture shows the lake clear, the right picture shows the same lake with a severe algal bloom. (Credit: Mike Quinn and Stephen Craven)

Brookmill Park Lake, a small lake in Deptford, Lewisham, Great Britain. The left-side picture was taken in September 2008, when the lake water was clear. Credit: Mike Quinn. The right side picture shows the same lake in October 2009, while in the midst of a severe algal bloom. Credit: Stephen Craven.
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