Going to “the lake” for the weekend is a ritual for many Minnesotans and Iowans. But lake lovers, especially those with pets or livestock, need to be aware of a potential hazard stemming from algae growth in lakes during summer.  What is an algae?  Small to microscopic plants.  Algae have world wide distribution and can be found in water, soils and air. Algae photosynthesize during the day and respire 24/7. Algae are plants so they need water oxygen and nutrients like phosphorus and nitrogen. Algae have a place in the food chain; Nitrogen & phosphorus feed the phytoplankton which feed the zooplankton & Shad which all feed the game fish. Under certain environmental conditions some algae species, called blue-green algae, can become toxic. Pets and livestock drinking lake water containing the toxic form of these algae may become sick and even die. Most algae blooms are harmless, but some blue-green algal blooms can produce toxins that may sicken people and animals. Blue-green algae are found throughout Minnesota and thrive in warm, nutrient-rich lakes.

How Can I Recognize It?

Algae occurs in virtually all lakes in Minnesota, but its concentration can vary considerably from lake to lake. It is most abundant during warm weather in water that is hard, alkaline, and rich in nutrients (primarily phosphorus and nitrogen, which fertilize aquatic plants as they do crops and lawns). Special characteristics of blue-green algae allow them to reach greater abundance than other types of algae. Some types of blue-green algae are able to use nitrogen from the air as well as other forms of nitrogen dissolved in the water, which gives them an advantage over other kinds of algae that depend only on nitrogen in the water.

Blue-green algae can use sunlight more efficiently than most algae. Some of them contain pockets of gas allowing them to float on upper layers of the water and out-compete other algae for sunlight. In nutrient-rich lakes, blue-green algae can become so abundant that they completely dominate other free-floating algae. The whole appearance of the lake water can be changed by these large concentrations of algae. This conditions is called an algae bloom.

These are the blooms that can occasionally become toxic. Toxic blue-green algae blooms are strongly influenced by the wind. Sometimes, the wind can completely dissipate a toxic bloom in just a short time (hours) or longer (a day or so). At other times, the wind increases the danger of a toxic bloom by concentrating (windrowing) the floating algae mats toward the downwind shore of a lake.

Most problems occur when the algae are concentrated around a shoreline and livestock, pets, wild animals and birds drink the water or otherwise ingest the algae. Toxic effects in animals can occur only when they ingest the contaminated water or algae. Farmers can suffer severe livestock losses from blue-green algae poisoning of their cattle’s watering source. This happened on Lake Tetonka in the 1800’s

An animal that has ingested toxins from an algae bloom can show a variety of symptoms, ranging from nausea and skin irritation to severe disorders involving the circulatory, nervous and digestive systems, and severe skin lesions. In the worst case, the animal may suffer convulsions and die.