Harmful Algal Blooms

Algae are microscopic organisms that grow naturally in oceans and freshwaters. Under certain conditions, some algae can grow into a large visible mass called a bloom. Not all algal blooms are harmful, but some species of cyanobacteria can produce toxins that can cause serious illness or death in pets, livestock and wildlife.

This indicator measures the occurrence of harmful algal blooms.

Blue-green algae in the Willamette River on September 16, 2014. Photo courtesy of Travis Williams (Willamette Riverkeeper).