The animal was found in the Water of Ken at Dalry by a fisherman at about 8.15 pm last Friday night.
And the otter had been caught in a Fyke net, which appears to have been illegally set to catch crayfish in the river.
Wildlife crime liaison officer PC John Cowan, pictured, said: “The setting of any unlicensed crayfish trap in Scotland is strictly illegal and irresponsible. As we’ve seen in this sad case, it also puts other local wildlife at risk.
“These nets are not designed in a manner to stop other animals from entering, becoming trapped and drowning. This is not the first time that a local otter has died in such a way.”
He is appealing for anyone with information on the net to come forward and contact police on 101, quoting incident 3426 of 2 October.