One plague of summer can frustrate  even the most diligent pond keeper - ALGAE.  Best known as long stringy algae to those who have suffered its presence in their ponds, this noxious form of algae thrives in the warm water full of nutrients that receives even modest amounts of sunlight.  Although algae is common to aquatic habitats, natural ponds do not have this particular form unless significant environmental problems exist, such as run-off containing fertilizers entering a pond.

Usually the typical fishpond that has high nutrients you can count on long stringy algae to show up each summer, and the worse the nutrient problem, the sooner it will appear.  Having lots of fast growing plants helps combat this algae problem, but they can take up so much of the ammonia and nitrate available.

Remove as much long stringy algae as possible.  It's much much fun - truth be told.  This messy, unpleasant task has to be done.  It would be better if you had managed the pond in the spring, the perfect time to create a healthy aquatic environment for the fish during the summertime.  Once you have removed as much string algae as possible treat the pond with Green Clean,  Algae Fix (by Pond Care) or Algaway (by MicrobeLift). Both Algae Fix and Algaway are similar but I tend to stick with all MicrobeLift Products since I know they have proven safe in my pond.  Pond Care Algae Fix is highly recommended by alot of pond owners.  The GreenClean works great also.  See the article on Green Clean.  After you treat your pond with the algae product next you would want to add MicrobeLift PL , active bacteria, which will help accelerate the decomposition of the dead algae so it will filter out.  Once you have the algae under control you can add a weekly dose to maintain. 

Having at least half the surface area covered with plants like water lilies, lotus and floating plants will help protect your water garden from summer-thriving algae by competing with it for nutrients.  Floating plants and submerged plants help combat this evil menace of the water gardener.

The main goal is to try and prevent algae from growing.  Aim to achieve a natural ecological balance in your pond, add more plants, and don't overstock with fish.