Running hot the temperature gage started going up?

Just left work in North Little Rock was driving home to Cabot Ark, got to about Jacksonville, which is about 10 minutes rom my job, and the temperature gage started going up, it usually stays at the halfway mark or a little below, but tonight it got to about the three fourths mark, so I stopped and put water in the radiator and got back on freeway, the gage went back down to around the three fourths mark and stayed there until the first Cabot exit which is the Heber Springs exit, so I took that exit, and drove the back way home, and then on my home it slowly crept up an got to the red mark on hot as I drove up in front of my apartment, what could be causing this problem?