Yeah, that's what I was afraid of - I figured if the water stopped or slowed flowing over the stoplogs the fish would stop or slow too. If you can figure out when this is likely to be happening, it will probably be repeatable though. When the water flows in or out of the lake rapidly, and there are enough stoplogs in to make swimming right in or out of the lake difficult, the bigheads will be stacking up like cordwood on the downstream side of the logs. Probably some bigmouth buffs mixed in.

Suckersticker - Swan lake is at the FWS refuge kind between the Illinois River and the Missouri River. It opens onto the Illinois River. You can see Swan Lake on Google earth. If you type in "Swan Lake" in Google Earth, it will zoom into a spot on the East side of the Illinois (I guess there might be a town by that name??). Swan Lake is across the river on the W side. You can see the outlet we are talking about on Google earth.