Different pools, different difficulties?

Hi all, All winter I have been swimming in an indoor 25m pool. I have build up from about 2000 to 4000m per workout over the course of 4 months (April-now). So this summer I found an outdoor pool which I swim in from 6-7:30 pm. I think the water is cooler than the indoor pool, and there are no lane ropes that cut down on turbulence (though there are very few people swimming laps there at this time). I do tend to go to the indoor pool about an hour or so earlier because of the crowd and because the outdoor pool has all-lap-swimmers at that time. But that shouldn't affect anything. The problem is that I always lack motivation and I have *yet* to finish a workout in this pool--for example, yesterday I was supposed to swim 3800m but only swam 1250 before I got tired and actually quit--and I've done this every time in that pool. I tried swimming the indoor pool the other day to test, and I swam the whole workout--4000m--without issue. What's the problem? Is it the water temp, the turbulence, both, neither, or something else? Or could it be mental? I love the outdoor swimming idea but if I can't swim my workout, I don't know how to fix it. Suggestions? :yawn: