bigmac,
I've had the same concerns and have done it both in the fall and spring. In the spring application, I didn't see any adverse impact to the spawning at all...but that is not to say it can't happen. I think the sooner you get it in the water, the sooner you will get the benefits. Remember to follow soil/water test recommendations as too much of a good thing is not a good thing.
Get cost estimates for the various options that are being offered. You will be surprised at how cost effective the spreader option turns out to be...if it is available to you.
