I would say some species of water primrose by looking at your first photo. I am used to a yellow flower though but you got the woody creeping stem. A good aquatic glyphosate will work(foliar treatment) with an aquatic surfactant. To control woody stem plants I go with Habitat now but 15 years ago we used Rodeo and had success. It may take a week or two to see the plant show signs of distress after treated.

Last edited by Coho Eddie; 05/16/16 08:49 PM.