Just south of the Big River RV Park and right next to the Big River INN is a decent launch ramp with parking. There is a restaurant right there called The Doc that has good food.
Sometimes the water does not rise until 11am or so and there are some real shallow spots so be careful. Up river by the dam is the cove and down river just above Lost Lake is shell beach (although I just learned it's not the real shell beach???).
Good luck