Waikato Regional Council is working with hydro generator Mercury Energy on safety issues after 21 year old Rachael Louise De Jong drowned this week.

Rachael was one of four people swimming in the Waikato River, when she was swept away when the Aratiatia Dam floodgates were opened.

The group were swept downstream and only three made it back to shore alive.

Power authorities open the Aratiatia Dam floodgates upstream several times a day.

In the summer, they are opened at 10am, 12pm, 2pm and 4pm.

A siren sounds before the water is released. There is fencing in place, and signs warning people of the danger and not to swim there. A siren sounds just before the flood gates are opened.

'Our hearts go out to the woman's family and friends and we're determined to look at what can be done better to prevent such deaths in future,” says Waikato Regional Council chief executive Vaughan Payne.

The Aratiatia Rapids. Photo: Greatlaketaupo.com

Mercury's operation of the Waikato River hydro scheme is regulated by resource consents granted by the regional council.

The operation results in spills from the dam, including for tourist display purposes and for operational reasons.

Sirens are used to alert people to the spills and it's understood the sirens were working at the time of the incident.

Under the council's navigation safety bylaw, the water 200 metres either side of a hydro dam structure is a prohibited zone.

That zone excludes unauthorised vessels and water-based activities from occurring, including jumping, diving and swimming.

'It's important that all people stay away from the exclusion zone around the hydro dams,” says Vaughan.

The council intends liaising with Mercury, the Department of Conservation, Taupo District Council and police over what's happened and any lessons that need to be learned.

'We want all river users to come home safe to their families at the end of the day. We put a lot of effort into supporting water safety and we'll work closely with our partner agencies over this incident.”