I find it interesting that an image survives of the Seminole War of a little-known event from the beginning of the Second Seminole War. (See below.)
General Scott ordered Major Read of the Florida Militia to send a command up the Withlacoochee River, to the first set of rapids, and establish a blockhouse of supplies. This was done under the command of Major McLemore. Once the post was establish, McLemore returned to inform Scott of the new post, but died of fever at Suwannee Old Town, and word did not reach Scott, so the General assumed that it was never done.
So the Florida soldiers were left forgotten at the blockhouse, and were besieged and attacked by the Seminoles for the next few weeks. The Seminoles nearly managed to burn down the blockhouse by shooting flaming arrows on the roof, but failed to totally torch the post. Weeks later, word of the besieged soldiers reached Governor Call, and he sent a command to relieve them of their duty.
This incident became a point of the board of inquiry between General Scott and Gaines, of the commanders failure in their campaigns in the war. Both Scott and the Florida commanders accused each other of neglect of duty during the war that resulted in the forgotten command at the blockhouse.
I was asked if I knew the location of the blockhouse, and this is my answer. (Probably one of the quickest responses I have given on Seminole War research, because I knew where to look.)
The blockhouse is shown on Taylor's 1839 map of Florida, just west of Fort Clinch but on the opposite or south side of the river. (The first Fort Clinch near what is today Dunnellon, not the later brick fort in Fernandina.) That would put it near where highway 19 crosses near Inglis. Unfortunately, the route of the river on a modern map is quite different due to the construction of the barge canal that was halted in 1969.
Sprague, pg. 150: Tells of Major Read with orders to go up the mouth of the river. General Scott believed the expedition was a failure, but then received word later on that there was a blockhouse. A letter from Call to Scott says,
"...A few days since I received a communication from Major McLemore, stationed on the Suwanne frontier, informing me that, under orders from General Scott he had ascended the Withlacoochee river, and erected a block-house on the south bank, some ten or twelve miles above its mouth, and that he had left a garrison of forty men in the block-house, and a large quantity of corn and pickled beef."
You can read the rest of the story of the forgotten men at the blockhouse in Sprague’s Florida War book, page 150-154. The commander (Maj McLemore?) who was suppose to announce the establishment of the post soon died of fever, and the command was left forgotten for a few weeks. I assume it was McLemore who died because we don't see any more of him in the war. The commander of the blockhouse company, Captain John Holleman, also died during the seige.
Looking on a modern map, 10 or 12 miles would put the blockhouse in Lake Rousseau, created as part of the barge canal. Any rapids would have been dynamited away for construction of the shipping path.
Woodburne Potter's book, "The War in Florida" mentions the blockhouse on the very last page, pg. 184:
"A small command of Floridians, which had been left by Major M'Lemore on the 5th of April in a blockhouse on the Ouithlacoochee, about fifteen miles above its mouth, were, by a strange oversight, entirely neglected, and they were assailed on the 12th of April, by a very large body of Indians, who attempted to burn the house by shooting fire-arrows into the roof."
If it was 15 miles from the mouth of the river, the location would still be in Lake Rousseau.
M.M. Cohen "Notices of Florida and the Campaigns" on pg. 230 says that the blockhouse is at the rapids, "within eight miles of the battle ground." I assume he is talking of Gaines' battleground which is mentioned on the previous page, and 8 miles to the west would put the blockhouse also in Lake Rousseau, west of where highway 41 crosses the river.
So from the various descriptions, they all seem to point to places that are now covered by Lake Rousseau, although the lake covers a wide area.