Hiding among the reeds and marsh grasses of freshwater bodies is a very reclusive bird called the Least Bittern. Least Bitterns are the smallest of the heron species found in North America. The bird has adapted to a life of hanging or walking on the grasses with large feet like a person on stilts. They are much more commonly heard than seen. 
The more common sightings of this bird are individuals who are flying from one patch of marsh grasses to another. This occurs usually around dawn and dusk, as they use the cover of darkness to stay hidden to avoid predators. The edges of lakes is an ideal place to start looking for one. If you can, stake out in a stationary location above the marsh or walk along the edge of your local pond.
The bird that is sometimes confused with them is the Green Heron. If you look at side-by-side pictures though, you will see how much lighter the plumage of the Least Bittern is compared to the Green Heron.
So, if you see a freshwater pond near you with marsh grasses on the shoreline, keep an eye out for this stealthy creature!