The reason the drainage area doesn’t go all the way to the bay is because the official drainage map uses the original shoreline, and areas that were filled in later don’t appear on any drainage area.
https://acfloodcontrol.org/the-work-we-do/resources/#explore-watersheds
The more I think about it, the more I think it makes sense to leave the official drainage map as is, and add a new place called something like “Temescal Watershed Extension” just for the filled area. Does that seem reasonable to you? You can probably make it yourself by drawing the shape during place creation. Let me know if that doesn’t work for you.
In terms of embedding observations, there are lots of threads in the forum discussing the project widget and other possible options. Here are a few of them:
https://forum.inaturalist.org/t/inaturalist-web-widget/14415
https://forum.inaturalist.org/t/observations-widget-is-not-working-anymore/7892
https://forum.inaturalist.org/t/documentation-for-observation-widget/11790