Probably because it is bordered on two sides by Camp Murry (National Guard) and Fort Lewis (U.S. Army) It was probably designated that way when the bases were opened for training purposes. Here is a historical article I found on Ft. Lewis.:
Fort Lewis, Part 1, 1917-1927
In 1916 Tacoma civic leaders promoted the development of a United States Army camp on the Nisqually Plain, located in Pierce County south of Tacoma. They succeeded in gaining War Department support and in January 1917 Pierce County voters overwhelming approved a bond to purchase about 70,000 acres and donate the land to the federal government for a military camp. In May 1917, Captain David L. Stone (1876-1959), Quartermaster Corps, arrived at the American Lake site to supervise camp construction. Hurley-Mason Construction of Tacoma started work on June 15. They erected 1,757 major buildings with a troop capacity of 44,685. On July 18, 1917, the camp was named in honor of Meriwether Lewis (1774-1809) of the Lewis and Clark expedition, and it opened on September 1, 1917. The Ninety-First Division, Major General Henry A. Greene (1856-1921) commanding, arrived and launched into rigorous training. The Ninety-First Division served with honor in France and as they fought, the Thirteenth Division trained at Camp Lewis, but then World War I ended and the division dissolved. Camp Lewis demobilized soldiers and then went into dramatic decline. Pierce County became concerned over lack of use and some even argued that the county should take back the land. However, the camp recovered and in 1927 a large building program made the post permanent and in recognition of that status became Fort Lewis. This is Part 1 of a two-part history of Fort Lewis, located in Pierce County, south of Tacoma.
American Lake
The Nisqually Plain, an area of prairies, forested lands, hillocks, and lakes, lies about 12 miles southwest of Tacoma. American Lake sits in its northern portion and around this lake the Washington National Guard held maneuvers at the end of the nineteenth century and during the first years of the twentieth century.
In the fall of 1916, as battle raged in Europe, a professional and businessmen’s military training camp was held at American Lake. This volunteer non-enlistment training program, organized by private civilians, encouraged citizen’s readiness. Among its cadets was Stephen Appleby, a Tacoma bank cashier, and vice-president of the Northwest Business Men’s Preparedness League. The League sought to attract an Army post to Pierce County. Appleby, who had been a captain in the Minnesota National Guard, understood the military process. He learned that an Army survey team would be looking for camp sites in the Puget Sound area, but the American Lake site was not on their itinerary. Appleby contacted the survey commander, Captain Richard Parks, and talked him into revising his September tour to include the American Lake camp. Colonel U. G. Alexander, the camp commander, headed up a welcoming committee to present the case for this camp selection.
Captain Parks was impressed and recommended the site to the commander of the Army’s Western Department, Major General J. Franklin Bell (1856-1919). General Bell then visited and, speaking before Tacoma business leaders, supported the building of an army camp here.
To read the entire essay, click on the link below.
http://www.historylink.org/index.cfm?Di ... le_id=8455
To download a PDF of the definition of Navigable Waters click on this link to a previous WWL.com post:
http://oregonfishingnews.com/forum/yaf_ ... aters.aspx