That's right: From June 3 to July 2, there'll be a post each day highlighting Teenage Mutant Ninja Turtles canon immigrants. Now, because TMNT canon is a little confusing, it can be hard to tell what counts as a canon immigrant and what doesn't. So for the purposes of this blog, a TMNT canon immigrant is anything (a) from the movies, cartoons, video games, toy lines, or tie-in comic series that later appeared in (b) TMNT volumes 1, 2, or 4 [because they're by the original creators] or TMNT volume 5 [because the original creators are involved, it's the new official continuity, and its goal is to use as much of the diverse TMNT lore as possible].
Dark Water is an elite military force that featured in the 80s cartoon episode "State of Shock" (October 1994). The episode features two members specifically: Colonel Knight and Sergeant Alex Winter. Winter was part of a super-soldier program that gave him electrical powers, after which he turned into the villain Megavolt.
Knight and Winter later appear in IDW's Teenage Mutant Ninja Turtles #52 (November 2016), and two issues after that, it's revealed they're working with Man in Black Agent Bishop.