Do you have a picture you could post?

Get some sort of squeeze bottle with a dropper type tip. This way you can squeeze the air out of the bottle while your above ground...and the as you carefully swim down to the bottom gently place the squeeze bottle tip near the "substance". Then suck some of the substance up into the squeeze bottle and deposit it into a glass jar.

Once it is in the jar you can let it settle for a day or so. After it settles you should be able to tell if it is pollen. If it isn't...could you get more samples?

do you have a full set of test results on your water?

thanks,
dan