These are some good insights Mat. I can't know for sure, but now that you mentioned the inlet stream temperature, that very well could be the major culprit for why we don't see LMB YoY like we used to 10+ years ago. Again, I should be more scientifically rigorous here, but the main inlet stream (coming off the mountain) is "cold", or at least colder than the still pond water. No idea of temps. In that vein, a big change regarding the inlet water and its temperature from the past is that the inlet water used to slow down and sit in a sediment pond (shallow, open, mud bottom) for a bit before it flowed into the main pond, so I imagine it heated up a bit in the sun. Nowadays that sediment pond is filled in with sediment, so the inlet stream just runs non-stop around the sediment island and continues flowing straight into the pond without slowing down, so it's feasible that this inlet water is now colder than it was in years past, when we did see more normal LMB spawning.

Can't know for certain that this is THE one and only cause, but the filling in of the sediment pond did correlate with progressively worse LMB spawns.