How do I get my Apple Watch Ultra to track my open water GPS location?

I swim in the San Francisco Bay several times a week. I purchased the Ultra with cellular connectivity primarily for safety purposes, thinking GPS tracking would be a piece of cake. The GPS has been way, way off on nearly every swim to the point I’ve shelved the watch. I’ve performed the calibration exercise to no avail. Does anyone know if I’m missing an update/trick?

[Re-Titled By Moderator]