I have some fish dreams too, like dreams about dark water with things lurking in it, and often I'm floating on something like a small or tippy log..
I think fear of the water and the things lurking in it must be instinct, and not as irrational as some people think.
Have you seen that TV show, River Monsters? And I think there have been some other similar shows recently too, with people getting eaten by sharks in freshwater lakes and waaay upstream in rivers.. so now I'm even more paranoid because the river near my house is not far from the sea, and one of the shows was in MY CITY, showing HUGE sharks that came 10 feet from the shore! I had no idea! Holy crap.
And once I saw something strange surface in the muddiest, murkiest part of the river, but I think it was just a sea lion. It was creepy but kind of cute, like a biiiig fat slimy dog with bulging eyes. I only saw it for a moment.
You really can never know what's under the water..
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"You gotta keep making decisions, even if they're wrong decisions, you know. If you don't make decisions, you're stuffed."
- Joe Simpson