Many of the ponders here in South Texas have the same issue. The pollen- accorns- oak tallows-- all contain tannins that will turn your pond into "TEA".

I often cover my ponds with a 1/4"inch netting from internetmesh.inc

it's the only size netting that can stop the oak tallows when the pollen drop is over. without it, the ponds I have are TEXAS TEA

c
my ponds