There are a lot of good points mentioned above. Many of the clear lakes I fish around here have matted vegetation growing in them, or are partially choked on the surface.
If the mats are large enough, and I'm in a boat, I will cut the motor as I'm approaching the mat and try to get on top of it, so it helps hide me from the fish below. Sometimes a paddle or a good set of oars will be crucial to get back out into the open water.
If the mat is thick enough and I'm fishing a weedless bait, I'll cast the bait on top, let it sit for a few seconds, and then drag the bait slowly off the mat so it falls over the side.