Rain usually improves fishing for smallmouth bass. The rain provides a disturbance on the water, which allows the bass to feed actively without getting spooked. Fishing is typically best with a light rain and a little wind. Smallmouth bass will feed throughout the day and they will be found much shallower on a rainy day.
The only time rain hurts the fishing is during thunderstorms or with a very heavy rain. Smallmouth bass like clear water and a heavy rain will stain the water. The thunderstorms can definitely spook the fish for a day or two, but this isn’t always the case. The severity of the storm definitely plays a role in how the fish react afterwards. A bad thunderstorm followed by a cold front creates the worst situation for catching bass. Bass can be inactive up to 3 full days after these situations. Some fish can still be caught, but it is a lot tougher during these conditions.
On rivers and streams, heavy rains cause a lot of runoff causing the water to become very dirty. Fishing is usually tough when the water turns a milk chocolate color, but some anglers do have success fishing current breaks near the shorelines following very heavy rains. Bright colored lures with vibration and/or lots of rattles will help get more strikes in the dirty water. Depending on the water levels, a heavy rain may provide some excellent fishing at the base of the dam. Although, if the water is too rough, fishing will be tough and it could even be dangerous.