Read and understood your query about your friend.
You're posting a good quality photograph would have helped me to answer in more appropriate way; yet, the information provided by you is indicating that there might have been brushed with some water creature with his leg causing blisters and terrible itching.
I would advise you in such a situation to give him some antihistamine and apply liquid povidone iodine to the local area and surrounding skin to avoid secondary infection and take him to the Doctor / ER / Hospital ASAP.
Hope this helps.
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