Ways an open water swim is better than swimming in the pool:
No chlorine smell
Out in the great wide open (kind of like running outdoors versus on a treadmill)
Better simulates race conditions
Not swimming in kiddie pee
Ways swimming in a pool is better than an open water swim:
Don't need a boat escort for safety
Nice little blue line to follow, no need for sighting
Much more convenient to get to the pool than to a lake
Not swimming in fish pee
I'm sure triathletes will give you more. These are just a few I was thinking about a couple weekends ago when I got in a couple good swims in both conditions. Also ran and biked that weekend but haven't done anything since. But I'm kind of sort of feeling my motivation coming back around.
7/2 1,000 meters in the pool at 2:23 or so per 100
7/3 10k at about 7:47 per mile
7/4 18.7 miles at about 18.7 mph (actually pretty good)
7/5 1,100-1,200 meters in Lake Wissota. 2:25-2:30?