Subject: What are orthophosphates & what do levels in indicate in fresh water?

We are conducting an experiment for our 10th grade chemistry final.  
In our experiment, we took samples from Lake St. Clair, and are 
finding the nitrate, orthophosphate, and pH levels of the samples.  We 
have been researching orthophosphates for over a week now, and haven't 
found anything relevent to our experiments.  Any information on 
orthophosphates that you could give us would be greatly 
appreciated.  Thank you very much for your time.

Re: What are orthophosphates & what do levels in indicate in fresh water?