Dark water and algae that we can't get rid of

We put in a fish pond in the fall of 2002. The water was nice and
clear until spring of 2003, when it got very green. We used Aquazyme
liberally (recommended by Southern States - the business that we
bought all our supplies from) from spring until winter. Even through
the winter, the water has remained dark and we can only see the fish
when they are at the surface. We have underwater plants, water
lilies, and other plants. Does anyone know of anything else to
restore normal water color?