Eddie, what's downstream from your pond? If the water from your emergency spillway goes to any creek or pond then the fish in those waters could most likely move into your pond during heavy rains.
bobad, where I live you can almost be sure Gams will show up in your pond. I can see how they would be more likely to be transfered by birds than other fish for a few reasons. They concentrate in the shallowest water where the birds wade, not deeper water where I would think most fish eggs would be. Also they're present all year instead of the seasonal occurrence of fish eggs. The fact that they are very aggressive might cause them to actively feed on or near birds feet. If fish with roe are transferred the eggs most likely wouldn't get fertilized, but since they're live bearers the gams have an advantage here too.
