I recently tested the DO level of rain runoff coming into my pond and found it to be 7ppm, pretty good considering my pond water DO level was a little low at 5ppm.

My take on what happens to the water inflow with respect to what it pushes out has most everything to do with temperatures of the inflow AND the lake waters. Cooler water sinks until it gets colder than 39 degrees F. Assuming that you do not have inflow colder than 39 degrees F andf your inflow is on the opposite side from the overflow...Cooler inflow would mostly push out the upper layer of your lake water...cooler water enters and sinks causing the upper layer at the overflow to exit. If the inflow is warm, it would not sink and most likely travel across the lake's surface and exit itself. There will be some mixing due to the turbulence and potential temp differences, but, in general, the above should be mostly what is happening.

Disclaimer: I do not have actual experience with the matter...just my book learning coming out. I am more curious about what effects massive inflow could have on turning a BOW over unfavorably...my little BOW has extreme inflow events on occasion.

As far as fish going over the spillway: Young fish seem to be more prone to that. I have heard that carp are more prone too. I stocked about 600 panfish in my 1/4 acre pond and have only found 3 HBG that have escaped to the yard/downstream ditch over the course of two seasons. I'm sure their were more, but surely not many more.

Fish on!,
Noel