Ponds get infested with algea and duckweed because of high phosphorus levels, which is often caused by fertilizer runoff from yards.  Rather than feed the problem by fertilizing your yard, here is an idea: 
Buy yourself a pump, and pump the water from your pond onto your grass.  In this way, the phosphorus and nutrient rich [...]

Continue reading about Rid your pond of duckweed and algea while greeening your lawn!