Diablo Lake is a reservoir on the Skagit River inside Ross Lake National Recreation Area, in the North Cascades of Washington, at 367 metres. It is part of the Skagit River Hydroelectric Project, operated by Seattle City Light. Its distinctive colour comes from glacial flour — rock ground fine by glaciers upstream and held in suspension in the water.
What drives the score here
That same glacial input keeps the water cold, and cold water is usually what caps the score at Diablo. The elevation is modest, so this is another location where trusting the air temperature would mislead you — the same trap as Lake Crescent, for a different reason. At Crescent the cold comes from depth; here it comes from what is flowing in. Steep terrain on both sides provides some shelter from broad regional wind, which leaves water temperature as the more consistent constraint across the season.
What the Paddle Score measures
A single number from 1 (Danger) to 5 (Excellent), built from wind speed and gusts, air and water temperature, UV index, cloud cover, precipitation and visibility — then constrained by fixed safety rules the model is not allowed to override. Wind above 25 mph costs two full points. Water below 5°C is penalised hard regardless of how good the day looks.
What the score can’t see
Diablo is a working hydroelectric reservoir. Levels and surface conditions respond to generation schedules, which the score has no visibility into whatsoever. A perfect forecast tells you nothing about what the dam is doing that afternoon.
Wear a life jacket, every time. The Paddle Score is a decision aid, not clearance to go out. It cannot account for your skill, your equipment, currents, traffic, or hazards at your launch site.