A diverse environmental community is composed of many different species living together and competing for resources in a "checks and balances" arrangement. Sometimes one species will gain an advantage over its competitors and flourish. Numbers of that species will increase until some resource becomes limiting and the population eventually returns to normal. For species that grow and reproduce slowly, humans for example, this process can take a rather long time. For fast growing organisms like true algae or blue-green algae, this can seem to happen overnight. We see this often on Missouri lakes. One day the lake will be beautiful and the next day the lake is green. It usually takes a few days or weeks for the lake to return to normal. Algae blooms will subside when a nutrient becomes limiting or if there's a strong enough wind to mix the top thermal layer of the lake (epilimnion). Viruses are also important in algal bloom regulation.
Both true algae and blue-green algae are capable of blooming and in some lakes may do so multiple times during a year. Green algae tend to be more prominent in the spring and early summer, while blue-green algae blooms are most common in the summer. Either type of algae is capable of blooming during any season, however. In Missouri, blooms of blue-green algae have been observed through fissures in lake ice.
Blue-Green Algae Blooms
Blue-green blooms are often accompanied by a film or scum on the surface of the water. Water with surface scums or films should be avoided by humans and pets. Blue-green algae blooms are typically green and often make the water look like pea soup or as if someone has spilled green paint on the water. Some blue-green blooms look like green curds floating in the water, others look like burgundy wine. Often, blue-green blooms will be accompanied by an "earthy" odor similar to freshly cut grass.
The dangerous toxins produced by some species of blue-green algae can be difficult to detect. A microscope is often required to determine if a particular bloom is composed of blue-green algae, and chemical tests to determine if toxins are present are traditionally expensive and time-consuming. Improvements are being made as the demand for inexpensive, simple analyses increases.
Even experts need tools to determine if lake water is safe to swim in during an algae bloom. The best plan is to play it safe.