The lake is difficult to access, but trails have been built to it and recreational fishing is allowed.

[3] When Mount St. Helens erupted on May 18, 1980, debris from an avalanche measuring 2.5 cubic kilometers blocked South Fork Castle Creek, creating a lake as runoff was impeded by the resulting debris wall which was 20 meters (66 ft) in height.

[2] There has been significant concern that despite the spillway construction, the debris blockage that created Castle Lake could erode suddenly, and create a flood posing significant risks to the communities of Castle Rock, Kelso, Longview, and Toutle.

[9] However, the conditions which created the dam are unprecedented, and therefore little to no historical data exists to support any conclusion regarding stability.

[9] The blockage appears to be stable regarding overtopping erosion, but the susceptibility to earthquake or hydrologic events remains undetermined.