If you have never been in a canoe or on the Anacostia River, you may want to make your first trip with the Anacostia Watershed Society.
The Anacostia has silted in and is shallow including Kenilworth Marsh. The marsh loses 90% of its water at low tide, so it is important to check tides in your planning. You can check tides at http://www.saltwatertides.com/dynamic.dir/potomacsites.html and click on Anacostia River. From there you can click on the Benning Bridge for the Aquatic Gardens tide, or Anacostia Bridge for the tide downstream at Anacostia Park.
To save yourself effort, use the tides and currents to your favor, riding the tide upstream and the current down.