What should I do about the weeds in my pond?

Information in today's blog comes from from the September October issue of Land and Water.  The article was written by Bob Lusk.  Lust writes that there are over 700 species of Aquatic Plants in the United States.  He says it may or may not be a problem to have some of them growing in your pond.  The first step in managing aquatic plants is to know what they are.  Identify the species if possible.
After you know your plants, then know your pond management goals.  If you have non-native or invasive species you probably want to get rid of them and start over.  If you have native species, do the plants help you meet your pond management goals.  Some plants provide protection to the shoreline.  Some provide good habitat for aquatic animals like fish and frogs.  Plants like cattails may provide good habitat for certain birds, but too many cattails my be a nuisance. Certain species of duckweed my cause problems.  Keep in mind also that too many dying plants can deplete the oxygen in your pond.   Lusk points out that you need to manage the habitat, not just the plants.  If you have undesired plants, keep in mind that you are providing the environment necessary for their survival. 
Read the whole article here.

This Purdue University booklet contains lots of good information on managing aquatic plants.