Is the water in the pond like a green soup?  Do you know what type of algae it is? Plankton algae makes the water turn green.   This  type of algae depends on two main things for growth,  sunlight and nutrients.   You can decrease the amount of sunlight available to the algae by adding more aquatic plants such as water hyacinths and water lilies. Nutrients in the water can come from water runoffs , fish wastes, decomposing plants, leaves, etc.,  and uneaten fish food.  If you see leaves fall into the pond , you can use a net to get  them out before they sink to bottom and start decaying and releasing nutrients into the water for the algae to feed on. Also increasing the biological filtration and the amount of beneficial bacteria  in the pond will help to remove the excess nutrient available for the algae to feed on.