Bad knee at 48 and I still want to run. Physio says swim. Does anyone actually enjoy swimming?

Left knee, ACL repair in 2011, meniscus trimmed in 2019. Ran 5 km every morning for 26 years in uniform. Now the physio says running is over and I should swim. I have tried the pool at the club three times. It is boring. I cannot see, I cannot hear, and I cannot tell if I am doing anything useful. I would rather do a hundred push-ups. Ex-servicemen and anyone else with a wrecked knee, what did you replace running with? Cycling, rowing, the elliptical, something else? I need the morning sweat. Without it I am unbearable, ask my wife.