The water is so clear because the algae has died off. The algae has died off because the Zebra mussel has lowered the oxygen level of the water. The lowered oxygen level also adversely affects the fish.
“The algae has died off because the Zebra mussel has lowered the oxygen level of the water.”
Nope. The oxygen level gets lower by the algae dying, the mussels eat the algae and make the water clear.
Young fish also eat algae and too many mussels mean very few fish can survive.