Greenery for me means, cover for fish to hide in. There are many forms out in the river in the form of lily pads, along with many species of grasses. Some of these grasses are native and some are invasive species. The fish will utilize the cover that whatever form of greenery is in the river to protect them as well as a great ambush point to feed on unsuspecting prey.
Here are some pictures of greenery from areas I frequent.