The Mississippi River is only about a mile or so from the south end. It does not affect Old Town. The ditch on the west side does flow to the White River but it has a spillway on it in the lake at HWY 44. It would take a catastrophic flood for the white river to back up about 10 miles of ditches and flow over hwy 44 and into Old Town Lake. What has the most effect on fishing is the ditches that run into the lakes from the farmland on the north and east side of the lake as well as if the spillway is open or not. If the spillway is open after a hard rain, you may as well load up your boat and fish the canal/ditch downstream of the spillway because they will shut down in Old Town because it is only 6 or 7 feet deep in the deepest spots. This depth is also the main reason why the fish spawn there before they do in other lakes in the area.