Wow lots of responses to the Q of why trout taste muddy and NONE right.
It's not from hanging around the bottom, not from diatoms or snails, not from
warm water, not from anything that has been mentioned.
One observation was correct though, usually the problem clears up over winter
and early spring trout taste better.
That's because their main diet changes. Chironomids (midge larva) hatch out of
the mud in the spring. When digested in large numbers the fat in the trout stores
the muddy taste of the little wigglers that hatch outa the mud on the lake bottom.

Now I know ya all want to know the CURE, so here goes:

Bleed and clean the trout immedictely upon catching and store on ice.

When ya get home skin the buggers using one of those crappie skinners,
remove mosta the fat layer.

Placed the skinned fillets in a glass baking dish with your favrite marinade sauce
to which has been added 1/2 cup of white vinergar. Marinate for 1 hr in fridge.

Take the trout out and rinse thoroughly for 10 minutes.

Then take the whole glass trey to the garbage can and DUMP contents
because there is no way to get the muddy taste out.

My personal method is to not kill the trout at all and to head for Safeway
after my trips and buy some nice Salmon or Halibut.

Get's the muddy taste out every time.