BLUE MESA RESERVOIR — In an effort to prop up water levels at the declining Lake Powell, federal water managers are negatively impacting recreation on Colorado’s biggest manmade lake.

That’s the message from Colorado water managers and marina operators at Blue Mesa Reservoir in Gunnison County. On Aug. 1, the Bureau of Reclamation, which operates the reservoir, began emergency releases. By the time the releases are finished the first week of October, Blue Mesa is projected to fall to its se...