Stonewort sp. A
7.6 km North, 1.7 km West of Hudson Bay
I believe this specimen is a member of the Chara genus, but at this time I cannot identify it to the species level (hence the sp. designation). Although it looks like an aquatic plant such as Ceratophyllum demersum (hornwort), Chara is a member of the Viridiplantae (green algae). Plants are believed to have evolved from some group within the Viridiplantae.
Specimens consist of a main axis bearing rhizoids at the base and producing indeterminate branches along the length. The main axis and branches contain whorls of determinate branchlets that bear globules (male reproductive structures) and nucules (female reproductive structures). The entire structure is encrusted with calcium carbonate deposits (hence the common name stonewort). According to Wikipedia, Chara are found in "less oxygenated and hard water and are not found in waters where mosquito larvae are present".