Trains are cool at first — they carry dots along a track and it’s pretty predictable where they’re going to go. Every move, the train will advance one space, no matter what else you do.
But with all of that movement comes difficulty with making squares and spreading water. So that’s a treat.
You don’t clear trains; you work around them. They suck. I got stuck on them for over a month.

Level 838: I’ve already started spreading the water around the level. The dark-olive areas are the train tracks.

Level 838: I managed to move the water onto the train — which is required if you’re going to complete the level. It’s not too hard on this level, but on some others it can be a nightmare.
Strategy:
Honestly, I still haven’t figured out a good strategy for trains. I’m writing this on December 13, 2016, and I’m only at level 885. I still have 25 more levels of trains to go before I can get to the next section, and once I get there I really hope that I get to leave trains in the past (and that they don’t somehow show up in a treasure hunt).
At this point, I do my best to ignore trains and complete levels around them. That’s about all I can say.
If this guide helped you out, please consider buying one of my books from Amazon. Here’s one: The Clockwork Russian and Other Stories, my first collection, which features two never-before-seen stories, including “The Clockwork Russian” — it’s an alternate-history detective story about a clockmaker, a disgraced policeman, and an evil land developer. It has some steampunk elements too.