Spotting

Purple loosestrife

The purple stuff is Purple loosestrife, Lythrum salicaria, and the green stuff its choking out is cattail, Typha species.

"Infestations result in dramatic disruption in water flow in rivers and canals, and a sharp decline in biological diversity as native food and cover plant species, notably cattails, are completely crowded out, and the life cycles of organisms from waterfowl to amphibians to algae are affected."

Does it smell good? It may be Lavender.