it’s an interesting theory since it’s been tweeted by one of the actors that they were filming while soaking wet. Or something like that. And that was round about episode 9 or 10 when we also know that Mary Margaret, Emma and Hook (and maybe Cora?) are coming back to Storybrooke. Could this mean they sailed on Hook's ship into the lake? There was also a water geyser in the new promo so who knows? I'm sort of hoping, since all the things lead to water, that this means there will be an episode on Little Mermaid, there was a point where the actress playing Cora said she turned someone into a fish!
Either way, I think the lake and it’s name could be quite important, so far none of the names in the shoe were chosen randomly!