Abstract: Employee #1 and coworkers were shutting down for the day an operation that involved installing heating blankets inside a gate that controlled in-stream water flow on a river. The heating blankets were necessary to prevent the gates from freezing shut. Employee #1 descended to the concrete spillway to secure a nylon tarp used to protect workers and equipment from high winds and water being blown over the top of the gate. The day before, the spillway had been dry and the covering of moss and algae was not slick. On the day of the accident, water had blown over the top of the gate and had made the moss and algae on the concrete spillway extremely slick. As he secured the lower edge of the tarp, Employee #1 slipped and slid into the water on the downstream side of the gate. An attempt was made to rescue Employee #1 by throwing him a lifeline, but the effort failed. He died as a result of drowning and hypothermia. At the time of the accident, the water temperature was 40 to 43 degrees F, the air temperature was 30 degrees F, and wind velocity was estimated at 40 mph to 45 mph.