I was thinking along the same lines as echoes.......wondering if there is any pollution that is new to the stream that hadn't been there before. Even if it's ground water fed, there may be something that is contaminating it to make the tadpoles die , thus, no frogs/toads, & dead trees.

It is so sad when our environment gets messed up. Humans can be so very destructive.

It may also be a change in weather patterns that can have an effect. I know that for several years in a row, we ended up with a drought right after I moved into my farm.....water was almost gone in the creek that runs in back of my farm. There were more deer in my woods, that came to eat what little grass I had, but they weren't there long. We have an extension office that is tied to the University & if you have anything like that in your area, you might talk with them & see if they know anything or may come out & test the water & the ground in your area.

Just a few thoughts & suggestions. I know how important the little creatures are that we are used to having & when they come up missing, it's a real sad feeling.

The one thing I don't miss that hit me the second year after I moved in were the 17 year cicadas.....they covered everything for about 3 months during the summer. They only come out every 17 years & when they do, the noise & the bother of them swarming around when doing anything out in the yard was horrible. They thought the sound of my lawn tractor was something to mate with I guess as they swarmed me so bad, I couldn't even mow my lawn that summer....yick.

Maybe there is a cycle thing that 's going on with the frogs/toads also....something you might look into depending on what species they are.

With nature there are so many possibilities.