Got a new lake dug and it's almost full. The spillway is about 6 ft wide. My question is should I put something like a small fence or something through it so when it runs over my fish won't go with it. There is quite abit of runoff so if we get a big rain it might flow over pretty fast. Lake is 1.5 acre if that matters. Thanks.
I wouldn't. Trash could build up on the fence and keep the spillway from doing it's job. Instead of fish, you could lose the dam.
Most fish go upstream in rising water. Some small fish will probably be sucked over the dam but the loss will be small.
6 ft seems a little small to me for 1.5 acres with a lot of runoff.
I did something like this to prevent fish from going through a 15" drain tube from one of our ponds. Dave is correct about debri potentially blocking the spillway if you put the fence right through it. I built a 12-ft square fixed dock over the pipe and placed the fencing on the dock posts. This provided me with 36 ft of fence that is 2.5-ft tall which provides much more surface area with lower flow rates through the fence. You could put posts in your pond so that the fence is extended into the pond and beyond the edges of the spillway. The trick is making something that looks ok. I added my fence when I kept finding lots of bass, cats and bluegill in a pool below the pipe after heavy rains. Like Dave said, I did not think they would dive into the pipe, but in my case, they did. I do not know how many washed away into the swollen creek below the pipe, but there were plenty left in the pool to rescue when the water went down.
urup,
Do you have an overflow tube on your dam? If you don't, you should, and that will limit fish loss in all but the heaviest flow events (assuming it is properly sized). As RAH says, that would be the place to put some type of screen.
Absolutely do not (repeat do not) put anything across your 6' emergency spillway. With a proper tube in place, the only time you would have water going through the emergency spillway would be a 25-50 year storm. When that amount of rain comes down at once, it will carry a lot of trash into the pond, and that would rapidly block a screen across the spillway.
If you're lucky, the fence wouldn't hold up and would wash over. If you're unlucky, the fence and trash hold, and water overtops the dam. In a matter of hours you could get enough erosion on the backside to loose your dam.
Bill