Hi PacOce,
Thank you for your reply here, I really appreciate it. 
It's probably going to be a long time before Niantic updates the map data they use for biomes.
It looks like Oquirrh Lake just a bit south of where you've been mapping has had several beaches mapped for a few years - I'd wager that if you take the kids down there, you'll probably find Wiglett much sooner than you would by adding beaches inside suburban water retention basins.
