Seawater from Wanganui's South Beach was sent away for testing on Thursday last week, after a mystery substance washed up there on Tuesday.
Health protection officer Margaret Tunbridge said samples went to the Institute of Environmental Science and Research (ESR) in Christchurch for testing.
It was a blustery day at the beach on Thursday, and Medical Officer of Health Patrick O'Connor went in up to his waist to get them.
The samples will be tested for enterococci, bacteria that survive well in seawater and indicate contamination with faeces.
Wanganui District Council and Horizons are also testing the substance to find out what it was.