Water testing such as this is only done by private laboratories. In the Eugene area there are two Delta Environmental and Analytical Labs. In both cases you have to pick up sampling bottles at their local offices, take the sample, and then return the sample within a certain time frame. In general the presence of algae does not indicate the presence of pesticides and other quality issues that would cause an issue with ducks. Raising ducks on a larger scale you would need to consider your rotational methods to ensure that the duck manure was being used by the grass and not allowed to run off into the seasonal creek.