As a young man, SCHS past-president Rick MacGregor heard his grandfather talk about the Army Corps of Engineers having dumped toxic chemicals into Aquia Creek for the purpose of killing an invasive species of water plant that was choking the waterway. Mr. MacGregor said that the treatment killed every plant in the creek and that it was years before the waterway recovered. Rick was long curious about what had happened and why, but wasn’t able to find anyone who could tell him. Finally, an online newspaper resource, Chronicling America, yielded information about an infestation of Japanese Water Chestnuts and the government program to eradicate it.

Around 1929, the water chestnuts were discovered at the mouth of Oxen Run below Blue Plains on the Maryland side of the Potomac River and by 1933 the plant was spreading rapidly. Also known as a water caltrop, the chestnuts grew on long stems, 6 to 14 feet long, with thick rosettes of leaves that floated on the surface of the water. These formed a mat of vegetation so dense that water birds could stand on top of them. The seeds, contained in barbed, spiny pods, collected on beaches making it unpleasant to walk barefooted in the sand. The chestnuts “crowded out the water plants ducks feed on, made useless the feeding grounds of fish, aided in the breeding of mosquitoes, and lately has gone so far as to impede navigation” (Evening Star, June 18, 1939). In addition to choking out the Potomac River feeding grounds for water fowl, it “destroyed the native species of vegetation which supports the life that forms an essential food for game fish. Many sections of the river are almost completely devoid of any plant life other than the water chestnut. Coves and tributaries of the Potomac River formerly well known for game fishing, according to the Izaak Walton League, now produce very few fish which may be caught from small boats. The thick beds of water chestnut collect large quantities of organic waste and create pollution hazards. This matter decomposes under the hot summer sun, with a resulting stench and unhealthful conditions, and in the comparatively stagnant water in the plant beds the mosquito breeds prolifically” (Evening Star, July 16, 1939). In an effort to control the mosquitoes, the Marines at Quantico used airplanes to spray the water chestnut beds with arsenic at ten-day intervals (Evening Star, July 16, 1939).

By 1939, various government agencies had decided that serious steps had to be taken to stop it. Researchers pointed out, “The Potomac River infestation has elements of national importance…If the plant is not eradicated…it will undoubtedly reach other great river systems of the United States and the fresh water bodies of the interior…The injury that would be caused if this plant got a foothold in the great duck feeding grounds in the nearby Susquehanna River and Upper Chesapeake Bay could hardly be estimated, and this menace is felt to be very real” (Evening Star, July 16, 1939).

Several experimental programs included the use of underwater mowing machines and rakes, underwater steel-bladed cutters, chain drags, rigs for removing the plants from the water for crushing or cutting, and poisoning (Evening Star, July 16, 1939). Because of the plant’s rapid growth and prolific seed production, the Corps realized that eradicating it would take a concerted effort over several years.

The Army Corps experimented with various chemical agents, including salt and unslaked lime, but the one that proved effective was a mixture of arsenic and sodium chlorate applied by spraying. “This method has no harmful effects on fish…The cost of this method is high, the period when it may be used is very limited, and there is a possibility of resulting danger to life” (Evening Star, July 16, 1939).

At Oxon Run, the Corps prepared to attack the chestnuts with a compound of arsenic and caustic soda that was said to be “non-injurious to fish in the quantities to be applied, but deadly to humans and livestock. The chemical is to be applied by spraying with specially designed equipment and falls on the plant in the form of a heavy fog. Within a week, the upper section of the plant will turn brown and finally sink below the surface of the water, where decomposition takes place.” The public was cautioned “not to get close to the spraying operations. Children, especially, should be kept away from the vicinity and not allowed to play in the water until the vegetation has disappeared. Livestock should be kept from drinking the water near the operation or eating the sprayed vegetation for at least 10 days after the poison has been applied” (Evening Star, June 18, 1939).

While poison was used initially, a study of the plant’s growth cycle resulted in the successful use of underwater mowing machines that cut the stems before the plants had an opportunity to bloom and make seeds. Even then, it took years before the water chestnut was fully under control.

By 1942 Piscataway Creek, just below Fort Washington, was pronounced clear of the pest. A newspaper reported in July, “This season more than 2,000 acres have been mowed. Hunting Creek below Alexandria is clear, as well as Oxen Run directly across on the Maryland side, and already eel grass has made its appearance in scattered places, which means the great rafts of ducks soon will return each fall to this area as was their habit before the advent of the chestnut” (Evening Star, July 2, 1942).

By 1947, the Corps had cleared more than 20,000 acres of chestnuts. “This was good news not only to boatmen, hunters and fishermen, but to property owners along the Potomac below Washington. At a number of points, property values have been affected by the heavy growth of the weed. The plant became so thick in many places that it interfered with fish propagation and forced out the celery and other water plants that wild ducks eat” (Evening Star, June 5, 1947).

Even then, though, the water chestnuts attempted to make a comeback. In the fall of 1954, a dense bed of about 25 acres was discovered in Days Cove near the Aberdeen Proving Grounds on the Gunpowder River. “Hundreds of thousands of dollars have been spent in efforts to control the water chestnut in the Potomac River during the past decade or two. It had taken over such famous fishing coves as Gunston, Potomac Creek and a host of others and was rapidly becoming a menace to navigation until the United States Engineers got after it. Although these extensive beds in the Potomac no longer exist, patrol activity to locate and destroy isolated plants or colonies is continuing, and may be necessary for unforeseeable years ahead” (Evening Star, Sept. 1, 1954).

Thankfully, the water chestnut hasn’t been seen in Aquia Creek for decades.