The down stream side is usually where the action is. Fish swim upstream to follow the scent of their prey. Swimming upstream, they are blocked by the lock and have to stop. They will congregate there realizing that occassionally there is an opportunity to continue their upstream quest. The hottest action should be when the lock opens and water rushes downstream. The fish are waiting for this and spring into action swimming upstream and feeding on any new goodies that appear. This is often one of the best places for the shore fisherman. Same thing with dams when they release water.

Always fish on the downstream side. Anytime I fish locks on the Cape Fear River in North Carolina, the fish get stacked up downstream. If you are allowed to fish inside of the lock, give that a try as well, as many stripers have been caught like this....something about all of that turbulent water makes them hungry.