Arrived hoping that all maps of the region were indeed flawed and that the confluence is not in the water, but on the lake's edge. According to the old bee keeper who lives some two kilometers from the confluence, the lake hasn't been itself since the eighties, and while we did not seek information about the confluence directly, the information he gave us about the distance to the lake made us sure we could get to the confluence.
We were wrong... Starting out on foot in reeds taller than 2m without any paths to follow and without water was a little bit of a mistake. We reached both 21 E and 41 N, but not both at the same time!
A second attempt will be made after August, when the snake season will be over.