As the former Director of Finswimming for the Underwater Society of America, I'm continually amused that divers in the United States do not know about the World Underwater Federation, and the sports associated with diving. These are sanctioned sports, with world-wide competitions. CMAS, or the World Underwater Federation, sanctions these sports. But in the USA, divers have not been interested. Competitive swimmers are beginning to learn about monofins, but not divers. If you want to learn more, here's some links:
What is Fin Swimming?
USA Fin Swimming
Sea Games 22--Vietnam
World Cup in Finswimming
I use longer fins, like those used for competitive freediving, for fin swimming in rivers. It builds endurance in the water, water ability, breathing techniques through a snorkel, and it is much less boring than lap swimming. Using a monofin in a pool is also fun, and you can practive underwater swims (not for distance, but for time in one or two-length swims (which is not hazardous if you learn the techniques, and do not hyperventilate; it's breath-hold underwater swimming for distance that's the killer, literally). Typical events in competition are 50 meter apnea (breath-hold), 100m, 200m, 400m, and 800m underwater swimming with a miniture scuba tank held in front of the finswimmer; and 100m, 200m, 400m and 800m surface snorkel swims. World records are extremely fast (under 15 seconds for the 50m apnea event).
We don't have to swim competition to enjoy finswimming as an exercise. He has great benifits, and increases dive fitness better than any other fitness activity. It is non-weight bearing, and so can be done at extended ages (I'm 57). It also does a great deal to strengthen the thigh muscles.
CMAS also sanctions competition in underwater hockey, underwater orientation, and spearfishing.
I do some light jobbing, hiking, walking and a lot of bicycling for my personal fitness.
SeaRat