Michael C Halls wig use

I've read that Hall wore wigs for the entirety of season 5 due to his ill health but I've just started watching again and the opening scene of SE05E02 Dexter is swimming in his pool and it looks like there's no way it's not his natural hair both underwater and when he emerges from the pool and shakes his head dry. Was it maybe still his hair in the early filming or was it just an extremely well made wig that you can swim with? I'm no wig expert so maybe they just can be that good