Upstream, in Lanark County, there are two sections of the river that are important for their plant communities. The first section of interest includes the east end of Dalhousie Lake and the swamp- and marsh-lined portion of the Mississippi River from the lake almost to Sheridans Rapids. Shallow lakes and adjacent river make up the provincially significant McCullochs Mud Lake Wetland. The second portion of interest is the rocky, rapid-filled section of the river from Sheridans Rapids down to just past Playfairville. Here there are small populations of unusual species including "Parnassia glauca" (Grass-of-parnassus), "Platanthera flava" (Tubercled Orchid) and "Spiranthes lucida" (Shining Ladies'-tresses).