kolk lakes

Kolk lakes are the remnants of an underwater vortex, or kolk, created when a rushing river or falls passes over an underwater obstacle, such as a boulder, and becomes a rotating column of water forceful enough to displace the obstacle, leaving a pit or basin behind. Once the river dries up, the impression remains, often filling with water to create a pond or lake. These are found in the Columbia River, where they sometimes support HABs.