Chuck as much as you like fishing on top off that stuff, there are more and bigger fish living below it. i have fished milfoil and hydrylla all my life, as deep as 18 ft. once the grass "tops out" there are two ways to fish it, on top like with the horny toad or a bunch of other "frogs and rats" that are made for it, or go underneath it, if your never fished below matted or topped out grass you are missing the boat. like i mentioned its not for everybody, but if your willing to work at it, and locate the better quality fish, remember big fish bunch up in summer just like they do in the winter, in deeper water with cover
summertime give me a deep diving crankbait for open water structure, and a big heavy 3/4 oz or more for deep thick grass, bass live under that canopy