Tired arms while swimming

The lifting you have done fore years is not sport specific related and irrelevant to spending time in the pool stroking 15-20+ per 25 yds for 30-60 min. You lack specific swim fitness, hence swim more...

Agreed, swim more and lift less. You may have well developed fast twitch muscle fibers, but you need to work on slow twitch. Time in the lake and pool are what will help the most.

About a year ago I asked this same question. The answer: Swim more.  I swam more.  The result: less arm fatigue. Therefore, swim more!

If I'm correct from some of your past posts, this is your first season getting into tri's. Your body is undergoing a lot of adaptations and working muscles and combinations of muscles that haven't been worked as significantly or in that way before, therefore, soreness will be the result.  The more your body becomes comfortable and strong with certain actions, then the less soreness will be there.  Now, correct form for all of the disciplines will also decrease the amount of soreness, so if you're working with a coach or other, experienced triathletes, have them give you some feedback on your form and you may find that you are doing something to aggravate the muscles in an unnecessary fashion.  Now, if it's that you're doing some technique piece wrong, and you adjust to the correct position, expect some different soreness as your body will now have to adapt to the new, right way of doing it.

Bottom line--adapting to the triathlon lifestyle requires an ability to get used to "soreness" (not bad pain...this is not about sucking up injuries) as your muscles and body adapt to the new demands and movements, or as you progress, increased demands and intensity.

For me with swimming... if my arms are getting tired... it's just telling me that I don't have my endurance back. That's all.

I also found that I have tired arms the first 800-1000 meters in my swims. After that my arms stop feeling fatigued and when I hit around 15000 -4000 meters I find my groove.

More swimming it is

I don't have soreness/DOMS in my arms they are just tired during the activity.  Every once in a while my lats will be sore but nothing bad, I can just feel them.

I would also add, just from my own experience not anythign I've read, that practicing out in open water (lake, ocean, etc) helps with this a lot. The turns in the pool give you a chance to let your shoulders rest. If you can get out and really find somewhere to swim continuously I think it helps a lot with tired arms.