For me, I've never been able to get over the internal conflict of wanting to build a useful tool like a map of fishing spots and releasing it openly, with the downside of good fishing spots getting overrun should the tool become popular. I also started working on a similar idea as yours a couple years ago, but for Instagram instead. It turned out the GPS tagging on Instagram was fairly inaccurate, and sometimes intentionally misleading, especially amongst anglers who tag incorrect locations since the number one no-no is spot burning.