Cold rain water maybe? Did you take the water temp over deeper water maybe? Early in the year you can have hot and cold spots in the lakes.

Ever go swimming in a lake in the summertime and hit a hot spot and then swim 12 ft away and hit colder water. Not sure why this happens but it does. LOL

I would have thought that the Upper Reaches of the lake (above Walls) would be warmer than the main lake deeper water areas.

It does depend on the amount of sunlight hitting the water and the bottom color and makeup along with the water's depth.

Up above King's Bridge should be warmer water due to the fact that there are a lot of shallow mud flats up there. So I am told.

Also the temp will vary during the day and the wind can also push water to one side of the lake. ie it may be pushing the colder surface temp water toward the windward bank. Wind also sets up currents in a lake. Wind pushes the water up against a windward bank and the water flows under the bank and back out into the lake. Sort of like a very mild undertow for those that have swam in the oceans. It's just a much weaker current. But enough to move cold water to the surface at times. Especially after several days of strong winds from one direction.

Regards,

Moose1am