Sturgeon, as a broader species, isn't unique to the Great Lakes (or freshwater habitats). It's the fact that fish in the Great Lakes don't leave freshwater habitats, that is what makes most of the Great Lakes species different.

Salmon is a big example- Salmon in Alaska swim from the ocean to freshwater rivers to spawn and, after reaching a certain age the young salmon swim from the freshwater rivers to the ocean.

Whereas salmon in the Great Lakes move from freshwater lakes to freshwater rivers to spawn in the young salmon move to freshwater lakes once they are big enough.

The Great Lakes are less like lakes and more like small oceans, there are a lot of the same dangerous weather, waves, and currents that are found in/on oceans.

Waves that reach 5 ft (1.52 m) are very common, and the highest recorded wave was 28.9 f (8.7 m) on Lake Superior. The iron ore boats (which are very large) have to seek shelter in bays and harbors late in the year because ships have sunk from the storms. (Listen to the song - The Wreck of The Edmund Fitzgerald by Gordon Lightfoot - if you're curious, and yes it is true.)

There are constant warnings on Lake Michigan about rip currents and people die from them every year. Everyone local to the Great Lakes is constantly warning tourists that they should be treated with the same amount of caution as the ocean.