If you have your HDS unit's sensitivity on "auto" then it is set at 100%. If you hit menu and uncheck the auto sensitivity then you can adjust the sensitivity somewhere below 100%. I normally run my units in the low 80's in weedy, algea filled water, dirty or stained water. Then in deep clear lakes I will run the sensitivity in the low to mid 90's.

Experiment with sensitivity in manual mode and adjust it in different water conditions. Then you can eliminate just enough of the "noise" or interference that clutters up the screen and see the targets that you are looking for.