I've been picturing 1 inch pvc and I'm not sure what the inside temperature could be on a hot day. I think the best way to accommodate a long pipe would be to bury it anyway which would take care of that problem. As long as the pipe wasn't angled sharper than about 40 degrees anywhere you could come out of the ground and up the back of a dam. You could also run it underground to a dock, then along the side of it and out over the water. I think it would concentrate some fish there.
If you want the larvae further out you could possibly support the pipe with something like "noodles" for flotation and run it on the water. You would turn the pipe up at the end to keep waves out and back down a short distance to keep rain out. A small amount of water in the pipe won't stop the larvae. Now that I think about it maybe you could somehow anchor the pipe below the surface so you don't have to look at it, and then turn up out of the water at the end. Anyway, you get the idea.
