Like GA said, many times they are referring to fishing into the feeder creeks and/or rivers of the lake. You will actually leave the "lake" and get into the flowing water of the creek or river. Lake Raystown, where I do the majority of my fishing, is almost 30 miles long and 195 feet deep at the dam. There are several smaller feeder creeks that flow into the lake, but the main river (Raystown branch of the Juniata) kind of just "becomes" the lake where the water is about 10 feet deep. You can go up river with a motor boat to the old nuclear reactor dam, about 2 or 3 miles past the lake. It is that stretch that is considered "fishing the river" in Raystown. In the lake we will fish the "old river bed." Just the terms we use locally for the areas we fish.