View attachment 78939
The red pin is the marina they got gas at, that is on the intracoastal. The Jupiter Inlet is just south of the red pin. They would have exited the marina and gone left into the inlet. Had they gone right, they would have remained in the intracoastal until they crossed under the bridge marked 811, west of there is considered the Loxahatchee River. The intracoastal continues south just below the 811 marker.
Just as a personal aside- My husband was born and raised in Jupiter; we just moved from there in January. He would not take a 19 ft boat through the inlet unless it was a flat calm day.