Husky A1-C pilot reported experiencing engine roughness; resulting in a return to the departure airport.

Narrative

During a local area VFR flight I decided to take the aircraft around a local monument and proceed south along a river. During the flight the engine started running rough which prompted me to aim for a field in the event of an off airport landing. The engine seemed as though it had a spark plug fouling issue. Not being able to make the intended field; I opted to deviate the flight toward the river in the event the aircraft engine did not clear.As I was running through the issue I continued to descend toward the river. When I selected the engine magneto to either the left or the right mag; it ran much better on one mag. I do not recall which mag it was; but at that point; I realized the aircraft was performing better and started to climb away from the river. While flying; the issue distracted me and I descended to approximately 200 feet above the river before climbing up to a safer altitude.I continued south down the river as it was the safest option with many fields to land in if the issue got worse; rather than climbing up to fly over a ridge line that did not have any options for a safe landing. I flew south down the river until it linked up with a highway which I could safely follow. Once over the highway; I continued to climb up to a safer altitude. While in flight the issue did not present itself again. I opted to continue the flight back to my home field where upon after landing I did a full run up while leaning the mixture to clear what I believed to be a fouled spark plug. The issue did not present itself on the ground. I will have a mechanic look over the aircraft before my next flight. Stupidly; due to the aircraft flying better; I had bypassed two airports on the way back to my home field of ZZZ that if I had to relive the event; I surely would have landed at either of those airports to reassess the situation sooner and more safely.