Hot summer weather brings out lake leeches

Recent sightings of leeches in Whitefish Lake have some residents concerned, but Whitefish Lake Institute director Mike Koopal says leeches are common in our local waters.

According to the “Montana Lake Book” which Koopal co-authored, “Leeches are found in shallow, protected waters and are active on hot summer days and at night. They are attracted to water disturbance around docks and swimming areas.”

Leeches may be doing exceptionally well this year due to warmer water temperatures that favors growth and reproductive success, Koopal said.

“The more sediment and nutrients that enter Whitefish Lake, the more favorable conditions will become for leeches,” he said.

The best way to avoid leeches, Koopal says, is to swim in deep waters. However, the lake institute has received reports of leeches swimming far from shore in the open water of Whitefish Lake.

“They’re surprisingly good swimmers,” Koopal said.

Only certain leech species are parasitic, attaching to mammals to feed. Other leech species feed on other invertebrates, according to Koopal.

Koopal recommends that if someone has a leech attached to them not to pull it off.

“Rather use an object with a straight edge or a thumbnail to break the suction,” he said. “Pulling off the leech or other techniques like applying salt or vinegar may induce it to regurgitate its stomach contents into the wound that could promote infection.”