Your question was one of my favorite science projects in 5th grade.
Our class went and pulled samples from several natural water sources. We then put a few drops of water on a glass slide and then added a cover slip.
The organisms we could see with an inexpensive microscope were fantastic. The teacher then had copies from the scientific texts for the most common organisms so we got to identify them.
I still have an old microscope with German optics from the late 50's. I used it with my kids many times when they were doing new science concepts at school.
I don't know if you can find a decent, old microscope on ebay at a good price. If not, a cheap, new scope from Amazon with Chinese optics might be sufficient.
These days on the new ones, I suspect you can get an attachment to the eyepiece so you can take a picture with your cell phone. If you post your critter pictures to Pond Boss, I am pretty sure our experts can identify your organisms ... and the rest of us can get a nice tutorial from your pictures!
Good luck on your analysis!
