Thank you for your query
Firstly i hope his swimming is clean and hygienic. Also he might have had a bit of urinary tract infection
which may have caused this problem. Ensure he drinks a lots of fluids. Also encourage him or you do it yourself to retract his prepuce (penile foreskin) a bit and clean all the whitish dirt (smegma
) in that region. You can apply some coconut oil or better still apply some antibiotic ointment. If the problem recurs get a urine analysis done and show to a pediatric surgeon.
Hope that helps
God bless you