What are Harmful Algal Blooms (HABs)?
Cyanobacteria are small microbes or bacteria that live in nearly every habitat on land and in the water. They have existed for billions of years as essential components of freshwater ecosystems and form the foundation of most aquatic food chains. When these organisms produce dangerous toxins, they are commonly referred to as harmful algal blooms or HABs.

When environmental conditions favor the growth of HABs and algae, such as warm temperatures and low or stagnant water flows, and excessive nutrient inputs, they can multiply rapidly creating nuisance blooms. Some HABs can produce toxins that can harm pets, wildlife, or people. Not all HABs produce toxins, but those that do can cause a multitude of health issues and even death. There are two types of HABs known as planktonic (HABs suspended in the water column) or benthic (HAB that grow attached to the bottom).

In the Lake Tahoe Basin, harmful algal blooms are most common during the warm weather months between late May through October, but they can occur all year.

The first known harmful algal bloom (HAB) occured in the Lake Tahoe Keys in August 2017. The level of measured cyantoxins was below any health concern, but the area was posted to protect pets. The Lahontan Water Board continues to monitor the California side of the Lake Tahoe  Basin for HAB issues and responds to reports of possible HABs by sampling the lake and posting results as appropriate.

Read about the Water Board's HAB response in the Lake Tahoe Basin.