Did you buy the saddle new?
Sometimes leather holds a bit of mildew, regardless how new it is and t can react with the sweat on your skin causing some serious irritation, and essentially "jock itch".
If you bought the saddle new and want to keep it, wear some longer shorts or wear cycling shorts which will prevent the chafing. Get some ketoconazole OTC (med for jock itch / ringworm / dermal yeast infection / athlete's foot) if you have a visible rash that doesn't clear up with a few showers and keeping it dry.
A big issue may be the pool you were in causing your irritation to really flare up. If your clothes were abrasive or shorts were really short and the leather was scraping your thigh, the chlorine and whatever else in the pool would certainly exacerbate the problem. The Brooks saddles are well worth the hardship, in my opinion. I have three of them and love them all for what they do.