Luke,
Search your local parks and wildlife website for answers.
Also. Here in texas, most of the lakes are owned and operated by the US Army Corps of Engineers. I suspect they are present in your state as well. Just about all lakes and parks surrounding them have some sort of influence from the corps. Since that's the case, I can hunt just about any lake. They recommend getting a permit but they never check it. A permit costs either nothing or 15$.
Some lakes around here also have state parks on them. These parks are owned and opertated by Texas Parks and Wildlife but the lake is operated by the Corps. This means I can approach the beach of a park by boat, stay in the water and hunt. Once I get on dry land, I am tresspassing on the Parks Dept. Metal detecting in state parks in Texas is forbidden and will cost you your tools if caught. You can get permission to hunt in a state park but you have to tell them exactly what you are looking for (an item you lost while there) and the eaxact area you plan to look in as they give you only a small area to hunt for it.
Doing a little research will go a long way in protecting you, your equipment and your hobby.
What state do you live in? I can get answers real quick.
Coolwhips