2003 Subaru Forester Temp gauge

While on the road with my 2003 Forester for about hour driving on the highway at 70 mph I ended up stuck in bumper to bumper traffic thru a toll & then a bridge for an hour. After about 15 min. In the temp guage started moving up to almost the red zone. I turned the heat on in hopes to keep from the red and seemed to work a little but then it eventaully it shot up over red. There was no steam & the engine seemed to running ok. Everytime I was able to move foward, the needle would go down to normal & then climb back up when stopped again. I coudn't pull over on the bridge cause literlly no where to go. This went on for 45 minutes untill we were over bridge and traffic was moving along again. The temp gauge was back to normal the rest of the way. I did notice clear water under the car after I was parked for awhile but no clloant. Checked the coolant level seemed fine, even in the resvior. Could this be water pumb issue or temp sensor issue?