You should do a more in depth job researching your own fears for this video. The water and dark confined spaces are very primal and passed down fears of humans.
The murky water obviously comes from millions of years of our ancestors at water holes having to contend with alligators, crocodiles, snakes, etc.
And the dark confined spaces is just darkness. Humans are generally... at lest uneasy in the dark because its when many predators came out and fact is, we're still more comfortable in the trees than we are on ground.
Also, that could have been a plastic bag chasing you. In water when you move it creates a drag behind you, meaning light weight objects will be sucked into this drag and "speed up" and turn with you.
Whats funny though, is your husbands fear is more warranted than your own (and mine btw, i wont go in dark water... fuck that, i watch too much nat geo. cloudy water can suck my asshole) simply because clear water is most likely referencing salt water, which has far more deadly things in it.
https://www.youtube.com/watch?v=olYnWXqM7YQ