Blue-green algae bloom on University Lake in Bloomington with typical surface scum. For their safety, people and pets should not into the water when such scum is present. Courtesy photo by Bill Jones
Blue-green algae bloom on University Lake in Bloomington with typical surface scum. For their safety, people and pets should not into the water when such scum is present. Courtesy photo by Bill Jones
Warmer weather brings people to area lakes for swimming, boating and fishing. But it’s also the time of year a dangerous type of algae can appear in the water that can sicken or even kill people, their dogs and livestock.

Signs warning boaters, anglers and others about blue-green algae are posted at several boat ramps at Lake Monroe, including Pine Grove, as well as the beaches at Fairfax and Paynetown.

While most algae are not dangerous, blue-green algae can be. All algae are classified based on their color, according to Bill Jones, a limnologist — a person who studies inland waters. The retired professor at Indiana University is an expert in lake and watershed management. The blue-green algae are a little different from most other types, because they are more closely related to bacteria than plants, Jones explained.

“They are basically photosynthetic bacteria,” he said, adding that blue-green algae are single-celled organisms that often group together to protect themselves from the aquatic creatures that eat them.

Another interesting characteristic of blue-green algae is their ability to regulate buoyancy in water, allowing the algae to rise to the surface to better use available sunlight and then submerge when temperatures rise enough to damage them. Because they can float above other types of algae, blue-green algae often can edge out other types of algae and plants.

“In the summer, it’s not uncommon to have blue-green algae as dominant in lakes,” Jones said. He’s helped test Indiana lakes as part of the Indiana Clean Lakes Program with staff and students from IU’s School of Public and Environmental Affairs for many years. Each year, routine sampling is done of about 80 lakes across Indiana as part of the program, which helps the Indiana Department of Environmental Management with a portion of the work required to meet standards set by the federal Clean Water Act.

It’s not only warm temperatures and sunlight that make algae grow in abundance in lakes, ponds and other waters. Nutrients including nitrogen and phosphorus can cause algae to grow at faster rates. Fertilizers that run off into waterways contribute to larger algae blooms in many lakes and ponds.

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