Narrow Leaved Cattail

Typha angustifolia, the Narrow Leaved Cattail or Lesser Bulrush, sends very long, narrow, upright blue-green blades out of shallow water and carries the familiar brown cylindrical flower spike above them in summer, with a short gap of bare stem separating the male and female sections.
It is a workhorse of reedbed treatment systems, where its nutrient uptake is the point, and it doubles as a dense screen at the water's edge on lakes and detention basins.
Narrow Leaved Cattail is a treatment plant that happens to look right at a lake edge, provided its spread is contained.