First off, are you sure it is hydrilla? My guess is that is is probably coontail or milfoil. Lots of folks mistakenly call coontail hydrilla.
As the other guy has said, the larger bass typically will cruise the deeper edge of the grassline whatever type grass it is. If you are fishing from the bank it may be hard to fish it properly. In the early morning or late evening, many times the larger bass will feed near the surface and you can catch them on a frog, buzzbait, or topwater plug.
When the hydrilla was present at Fork, one of the most effective ways to catch bigger bass during mid-day was to fish a heavy jig or t-rig worm on the deeper outside edge. Many times that was in 14-16' of water. We weren't "punching" the grass but rather going down the deep edge following it on the fish finder unit with the transducer mounted on the troll motor.
One of the largest bass I ever landed on Fork came from Little Caney in early August mid day on a 3/4 oz jig in 14 feet.