Canadian producers Jean Mathieson & Al Guest attempted to reimagine Jules Verne's Captain Nemo as a heroic character, but the 5:00 shorts that aired on Captain Kangaroo in the US and Popcorn & Friends in the UK didn't last very long.
The Undersea Adventures of Captain Nemo bowed in 1975, and would, I believe, be a recurring feature on Kangaroo, at least, for the remainder of the 70's. Captain Mark Nemo (Len Carlson) piloted a smaller version of the Nautilus, aided by a pair of young assistants, Robbie & Chris (both voiced by Billie Richards), who served the same purpose here as Wendy & Marvin did on Super Friends over on ABC, acting as an analogue for the children watching at home as they learned about undersea life and its dangers. The episodes fly by, such that if you blinked, it was over.
Magicshadowsinc. uploaded the series opener:
EastWest has released at least a couple of volumes on DVD, easily acquired at the local dollar store. You may want to have some books on oceanography handy after your kids watch the videos.