about the last week in October, my stream, aqueduct and canal system became clogged with autumn foliage so I shut it down but left water in the pond and canal (but not aqueduct) so that my frogs can overwinter in the silt below, where I'm assuming they're at (maybe someone can tell me). I look forward to seeing the frogs and tree frogs next spring!
Oh, the reason I shut it down is b/c the leaves were clogging the very small outlets that move the waterways from one system to the next and most of the system has trees over it (for shade as it gets darned hot in summer here!)