Pretty general advice really (from an MD):
Firstly, you go to the top of my xmas card list for donating a kidney, imagine it is a close relative etc. They will be eternally grateful. Mega kudos. Thank you.
Advice:
1. Avoid dehydration
2. Be careful with ultra distance events and situations putting you at risk of rhabdo
3. Be careful in hot races
4. Avoid anti-inflammatories when you may be at risk of dehydration

This guy did an altruistic donation and continued to race long course. https://exitrowiron.tumblr.com/search/kidney

And through his website I also found this: https://kidneydonorathlete.org/

  
I had an atrophic kidney removed 8 years ago and suffer no ill effects. Always been a mega hydrator and am sticking to that program for sure. Good on you!

First. I applaud your generosity. The world sure could use more people like you.

Second. Just remember that Greg Lemond has only one functioning kidney and that didn’t seem to slow him down. Just follow your Dr’s recommendations for recovery returning to racing.

I'm a Uk based kidney transplant doctor. Have sent you a DM

no idea, but you're awesome and please keep us updated as to how you're doing post-surgery if you decide to donate.

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maybe she's born with it, maybe it's chlorine
If you're injured and need some sympathy, PM me and I'm very happy to write back.
disclaimer: PhD not MD

Please, don't anybody consider me a saint. I didn't say I was donating anything to anyone. Just the "ask" scared the crap out of me. I don't even know how to respond to his email.

I was just looking for some info on how this affects someone that considers themselves an endurance athlete.

Fwiw, I don't even donate blood! And I know I should.