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Harmful Algae Blooms (H.A.B.s)

Written by guest author Gabby Pfeiffer

Harmful algae blooms (HABs) are a serious threat to the lake’s health and water-based recreation. That murky green film can have serious health impacts. Some cyanobacterial blooms (harmful algae blooms) can cause harm to your skin, liver and nervous system. Adequate exposure to the harmful bloom can cause a variety of symptoms in both humans and animals. In fact, every year nationwide there are accounts of serious illness and death of dogs. If your dog does come in contact with a HAB be sure hose them off quickly before they can lick concentrated toxins on their fur. These HABs can be expensive and difficult to treat, which impacts industries that need clean water, like recreation and irrigation.

But what causes HABs? There are a few main causes in freshwater: excess nutrients, warm temperatures and lack of circulation. While nutrients such as phosphorus and nitrogen are essential for plant growth and are helpful fertilizers, they (particularly phosphorus) can be harmful when entering the water. Nutrients have similar effects on algae as they do on the plants in your garden where they support and accelerate growth. The algae in the water will multiply rapidly by using excess nutrients and absorbing energy from the sun’s heat to continue reproduction.

Rising temperatures in our area don’t help the issue. The warmer water creates a more hospitable environment for cyanobacteria. When you combine excess nutrients and high temperatures in a low drainage lake, you have the perfect scenario for an algae bloom. Our own Fernan Lake struggles with chronic algae blooms every summer and becomes unusable for the duration of the bloom. Because of these factors, you'd think that the smaller lakes would bloom, but there are large lakes that bloom as well.

Lake Coeur d’Alene experiences HABs in the southern region of the lake. HABs increasing throughout the lake are still a major concern due the unique history of the lake. This is due to the historic mining done in our area, which released heavy metals into our lake such as zinc and lead. Currently most of the metals are bound to sediments by an oxygen cap just above the floor of the lake in the overlying water. However, an algae bloom could degrade this oxygen cap after the bloom dies and sinks to the bottom. The process of decomposition of the algae requires oxygen which erodes the cap between the metals and the contaminants

There are a few things we can do as citizens to help. First, be aware of what you use in your gardens and lawns. Fertilizers are a useful tool, but overuse or carelessness can cause overproduction of algae and harm our water. Look into no-phosphorus fertilizers and lawn treatments and avoid over-irrigation of lawn and gardens where fertilizers end up in waterways. Second, respect the drain. Storm drains south of I-90 go straight into the lake, so be mindful of your water waste. Avoid washing your car on pavement, instead do it on a grassy surface or take it a professional car wash. Pick up pet waste in your yard and on your walks with your dog. Don’t leave yard waste or garbage in the street as it can seep into storm drains. A good rule to live by is “only rain down the drain”.

Currently there are active health advisories on Fernan, Cocolalla, Spirit and Avondale lakes as well as in Morton slough on the Pend Orielle River. If you see widespread scum along the shoreline of any other lake, please call the Idaho Department of Environmental Quality.

University of Idaho

Physical Address:
1031 N. Academic Way,
Suite 242
Coeur d'Alene, ID 83814

Phone: 208-667-2588

Fax: 208-664-1272



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