I think it also has to do when the trout go on a snail eating binge... and it's also from what the snails were eating too.

I've always found this to be true for lakes where snails are a big part of the food base for trout. About April 1st they start tasting muddy.

The Sage lakes over in the seeps are ones where I gave up keeping trout past April 1st. Lots of snails in the lower lake.