Montana Department of Environmental Quality
2d ·
As we approach the holiday weekend, it’s a good reminder to be on the lookout for harmful algal blooms (HABs) so that you and your pets can avoid exposure. The organisms that produce HABs (cyanobacteria) are a natural part of Montana’s waters, but when conditions are right, their populations can grow and potentially release toxins into the water. Low water levels this time of year can increase the presence of HABs, especially in areas of shallow and warmer water.
HABs may look like spilled paint, globs, grass clippings, or surface scum. When in doubt, stay out of the water where HABs are present to help keep you, kids, and pets safe. Visit hab.mt.gov to report and track suspected HABs.
Reports in the last week:
Tongue River Reservoir, Big Horn County (confirmed 8/26/25)
Homestake Lake, Jefferson County (confirmed 8/26/25)
McGregor Lake, Flathead County (confirmed 8/25/25)
Holter Lake, Lewis & Clark County (confirmed 8/23/25)
There are continued reports on several waterbodies throughout the state.
Source: Montana DEQ
