I swim for 2 hours before I run out of time but not out of "steam"

(-we have 2 hours* of "adult swim" in the morning) My laps take about 90 minutes, depending
on how much I talk & goof off, and how many fast laps I feel like doing. I like to use the last half hour for other exercises (like "rowing" with my water-weights, etc).
BTW, I only swim with fins...you get a much better work-out that way (you're pushing more water). *In later summer we'll get 3 hours adult swim in the morning, &
by then I'll be 'ready' for it.
Our pool is 25 meters (half Olympic size) and a "lap" is across & back (50 meters). Each mile is 32 laps, so keeping track of 64 laps (2 miles) I make use of the "rope"
that divides the lanes; the "rope" is actually a cable strung with plastic disks, so each time I start a new lap, I move one disk over, like a giant abacus...

I start
over for each half mile, it works better that way.