Instructor Pilot with Trainee reported while performing maneuvers the engine began to run rough with a loss of power. With assistance from ATC the Instructor diverted to a nearby airport. Fuel contamination is suspected by Maintenance.

Narrative

I departed with my student from ZZZ1 in our Cherokee PA-28-180 for maneuvers in the ZZZ practice areas to prep for his PPL checkride. We requested flight following from ATC; and maneuvered in the area. After some time; we descended to around 1;500 ft. MSL and began setting up for ground reference maneuvers over the breakwater. We felt and heard an immediate loss of power; with the engine seeming to drop to idle power. The aux fuel pump was already active due to maneuvers.I immediately pitched for best glide and ran the restart checklist; switched fuel tanks and power came back several seconds later. We started a climb and towards ZZZ; [requested priority handling] to ATC; and landed ZZZ Runway XXL uneventfully.Once on the ground; I ran on the suspected fuel tank for several minutes until the engine roughness stopped; and we had the plane inspected by the local A&P. No issues were found; leading me to believe there was contamination or other contents in the fuel that cleared out; and once the A&P ok'd the plane; we returned it to ZZZ1.