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.