I have looked in the Chronicles and the battle has only been addressed twice in the issues that have been digitized. In V. 9 #4--Dec. 1931 the battle is discussed in an article on Opotheleyahola. There is no direct mention of a swamp, but on p. 449 Col. Cooper is quoted a bout the Confederate troops extricating themselves from the matted swamp grass, after the fight. In the second article in V. 18 # 3--Sept. 1940, on the war in 1861 there is no mention of a swamp, but there is a contemporary map that gives the battle's location. With this information I have done a google map search. If I have the correct spot, there are several areas on the peninsula that Opotheleyahola's camp occupied that could be swampy under the right conditions (even after the efforts to control flooding). So you know, the area I'm looking at is North of East 86th St. North & West of North Delaware Ave. I know this is not solid evidence but it could help you find more resources.

Robert