While Washington Channel is known for its fishing, it’s not because it’s a particularly inviting habitat for fish species. Instead, its unique flow pattern of imported water make it a “trap” for fish swept upriver by the tides, and as such it sees fish species that aren’t typically found in other local waters — which, oddly, makes it popular among anglers.
The most productive and diverse habitat in most waterways–the shorelines–are along the Washington Channel entirely armored with concrete. Beyond those concrete walls are monocultures — either more concrete or lawns, rather than on-shore wetlands. Between the walls, the constant scouring effect of the Channel’s twice-daily flush keeps the Channel relatively deep, so there are scant near-shore wetlands: the central channel is kept at least 9-14 feet deep for navigation purposes, but the entire channel ranges from 3-26′ deep. (The Tidal Basin is a bit more inviting to life, since it’s shallow [5-7′ throughout, average depth of 6.5 ft.] and a bit more placid.) The shallow-water ecosystems at the water’s edge, which combine sunlight, warmth, nutrients, and shelter, are largely absent along both. The Channel is, in effect, a concrete canyon.
This canyon isn’t very resilient, either; it can easily flood, as there’s nowhere for water to go when the river rises — or even for the wake from powerboats to do anything other than echo off the walls.
The shore edge’s armor has started to degrade, though: a combination of higher water levels, subsidence by the marshy soil, inevitable concrete failure, and erosion means that some areas behind the seawall are now almost permanently wet. Some wetland species might start to colonize these damp pockets, although lawnmowers will probably thwart their progress.
Some of the shallower parts of the Washington Channel have demonstrated potential as rich habitat, though. A stretch of older seawall along Fort McNair, beginning in a small lee behind the Titanic Memorial, is a comparative haven for aquatic vegetation and fish. At one point, there was a 10-20′ wide band of submerged aquatic vegetation (SAV) off the fort’s shore — which, according to the NOAA navigation charts, is the shallowest part of the Channel at just 2-5′ deep. These underwater meadows provide valuable fish habitat, particularly for anadromous (half-ocean, half-estuary) species that spawn there before returning to the saltwater estuary downstream.
Even as Potomac River water quality has improved, habitat quality in Washington Channel remains poor. The quantity of SAV (much of it invasive hydrilla, which was still better than nothing) grew substantially in the 1990s, alongside large fish populations.
Sadly, major rains throughout 2003 — when the Potomac carried more than 3X as much water as in the drier years 1999-2002, and twice its annual average (MWCOG/VT PDF, pg. 32-33*) — led to severe sediment and nutrient overload throughout the Potomac ecosystem, and thus to large algae blooms in 2004. These two years’ trials devastated established SAV in the upper Potomac estuary, including in Washington Channel, and so far neither plant nor animal life seems to have recovered.
Second chances: improving habitat in channelized waterways
While the Washington Channel may be the local champion for having the least natural stream banks, it’s sadly far from the only such watershed nationally. Perhaps the worst example of an “imprisoned river” is the Los Angeles River, almost all of whose banks were paved back in 1938.
Yet nature does abhor a vacuum, and so if you provide adequate habitat (as the Channel did for those few lovely years around 2000), an ecosystem will soon blossom. In Chicago, the Friends of the Chicago River built a “floating fish hotel” to provide a smidgen of near-shore-wetland habitat within downtown’s urban canyon, and plans to significantly expand upon this experiment in the near future.
* Incidentally, to update something I wrote earlier about Western and Eastern water systems, the Colorado River’s pre-diversion annual flow was 50% larger than the Potomac’s average flow (at Little Falls) today. It would rank among the largest Eastern rivers, like the Hudson or Susquehanna. This great map from the Pacific Institute clearly shows my earlier point: the East is well-watered indeed.
** 2018 update: a SAV planting program has succeeded in dramatically increasing SAV in the upper Potomac estuary since 2013, and in increasing juvenile bass populations. Floating “fish hotels” have been added next to the 7th St. “recreation” pier at the Wharf.
This semester, I’m taking a Natural Resources class through Virginia Tech about understanding local watersheds, wherein I’ll be researching and posting knowledge about the Washington Channel. You can explore the other watersheds that my classmates are investigating over at the class blog’s page. Other posts in this series can be found using the tag watershed.