Cessna 150 Pilot reported a drop in engine RPM and continued fluctuations during flight. After utilizing carburetor heat with no improvement; the pilot diverted for a precautionary landing.

Narrative

I was flying a Cessna 150M from ZZZ to my home airport of ZZZ1. I was at 4;500 ft. MSL in VMC when I noticed a 50 RPM drop. I thought the Throttle slipped out some so I reset the throttle and pulled the carb heat in case carb ice was forming. A minute later the engine started to vary RPM between 1;800-2;400. I went through my rough running engine checklist. I believe this was carburetor ice that had formed. After going through the checklist I advised ATC on ZZZ Approach. Approach offered vectors to ZZZ2 and ZZZ3. I decided ZZZ2 was not an option due to open water. I decided ZZZ3 was not an option due to the lack of available landing options enroute to ZZZ3. I decided to land at ZZZ4 as it was the closest airport near me. I flew over the airport and spiraled down. Entered a downwind pattern and performed a landing with partial power. 15 minutes later I performed an engine run-up. The engine made full power. I then decided to call it a day. The next day I performed several full power run-ups without issue. I then took off without issue. In the future I will cycle carb heat periodically and watch for an RPM rise/rough running engine due to ice melting while at cruise to ensure carb ice isn't building again.