The type of fish kill that happened in Elkhorn happens every few years. Diquat and Cutrine are not toxic to fish or humans themselves. However, their application to surface waters can kill so much algae (single-celled and multi-cellular) that the decomposition of the dead plant material increases chemical oxygen demand (COD). COD suppresses DO (dissolved oxygen) levels to below that needed by trout.
It is interesting to see brook trout are among the dead. They are tough little devils that can usually survive very low DO levels.
Weed control contractors understand the toxicity of their products but they sometimes do not consider COD.
Steve Fisher
Ketchum
Editor's note:
Several state agencies are investigating the fish kill in Elkhorn Creek on May 31. While preliminary evidence suggested the cause might have been the use of herbicides and algaecides by a private contractor working for the golf course, no final determination of the cause has been made.