I mention it because it was the 'thing' at the time, but I'm not sure if you want to do that for the play table. She's surely want her dino's to swim, and if you fill it with a resin, she'll not be able to dip them in much, and they'll be back to skating across it or dancing on top of the water level and pretending to swim, just as you surely did with the painted rivers.
Hmm - maybe a quarter inch or thin layer of resin on the bottom, a suggestion of water that leaves your trough available for more dipping, but makes the river look wet? Wet ish?
Clear resin is the direction I was going, but a 'skating problem' isn't something I had considered before. Thanks for that. I'll keep Jenny posted and get her input. Layering in a few fish near the bottom is a great idea, actually, since I had been planning a 'pterosaur aerie' for the mountain and Jenny's big on Pteranodons and Rhamphorhynchuses dive bombing for fish.