I just emailed a customer who asked about algae blooms in Florida.  They wanted to do an experiment.  Here is how I responded...

Hi Glen and Daughter,

Great experiment concept and line of inquiry. Yes, we get this question often. Best way to approach is to ask your daughter, what she is observing. Then start asking why. When she can't get the answer from the internet, or from you,  then create SIMPLE logical tests to answer her question.

Here are some examples of: is my local water replete (nutrient rich) and can result in an algae bloom?

Experiment: gather water from your area and evaluate it for growing algae. (culture a few bottles of local water with and without f/2 nutrients- If the bottles grow identically, then the water is saturated with nutrients and can result in a bloom. If only the bottles that were given the f/2 algae nutrients bloom, then the water is not eutrophic.)

You can determine nutrient levels using test strips (go for nitrate and phosphate). Creating a map for your local waterways. (nothing I sell, but it is really cool).

I hope this helps,
Matthew