Thamar Nanette Henneken (born August 2, 1979 in Delft, Zuid-Holland) is a former freestyle swimmer from the Netherlands, who was a member of the Dutch Women's 4×100 m freestyle relay team that won the silver medal at the 2000 Summer Olympics in Sydney, Australia. She did so alongside Inge de Bruijn, Wilma van Hofwegen and Manon van Rooijen.
After the Sydney Games she tried to succeed as a rower, but she soon returned to swimming. She is engaged to former world champion Marcel Wouda. The couple had a baby in early 2005.