The Cohoes Wave just off of Fulton Street in Waterford, NY is a well-known spot for kayaking, because the ruins of man-made features create large standing waves. A standing wave occurs when the underlying structure of the riverbed causes water to quickly rush downstream, leaving a void into which an influx of water is actually rolling back upstream on top of the downstream rush of water. The wave remains stationary, but is otherwise not unlike an ocean wave at the beach. Surfers have long sought places in the world where standing waves form.
I drove down before work and took a look at it. The gauge height according the the USGS conditions report was at 12.25'.
The water seems rough and scary looking, and is probably out of my league (at least on a day like today). 1000' after the wave, a large dam drops off, so one needs to be very careful in a place like this, like maybe by refraining from kayaking here. The following satellite photos show the Cohoes Wave. The image on the right is zoomed out to include the dam after the wave. Click on the images to view an interactive version.
To add to the other dangers, the water itself is some of the more polluted water in the area, so it's really not the first place I would go intentionally dunking my head on a warm summer day.
A video does a better job of capturing the turbulence in the water than a photograph does. The wave is on the right side. You can see the water rolling backwards upstream, forming the standing wave:
* Photos, Video, and Comments about Kayaking the Cohoes Wave from americanwhitewater.org
* Several online discussions about the Cohoes Wave
* Pictures of Kayaking the Cohoes Wave from RPI's Outing Club
* Current USGS Statistics for the area
* Youtube video of surfers on a standing wave in Hawaii