Can anybody help me identify these weeds, and what I can do about them?
THANKS!

Welcome to the forum!

If you crush some in your hand, does it smell somewhat like a skunk?

Best way to ID the plant/algae is to take a single strand, place it on a contrasting background (white paper, or something else) and take a good clear close-up of the strand. That will help greatly.

If you want to try to ID it yourself, look at this site:

http://aquaplant.tamu.edu/plant-identification/

Steve - your photos were taken too far away from the subject or out of focus to be of much benefit for ID-purposes.
Based on the last photo alone, I would guess the organism as either Nitella or bladderwort. One is a form of algae while the other is a plant (respectively), so an accurate ID is absolutely critical for devising any control-measures or tactics.
Better (focused) close-up photos of a single strand should allow an easy ID.