Participants could give many free activities a go including snorkelling, water skiing with the Kai Iwi lakes Water Ski Club, waka ama with Hikuwai o Kaipara Waka Ama Club and water jogging with Sport Northland.
Kevin the Koi Carp shows Blaze Nicholas, 6, how to identify a koi carp and explains why he needs to help keep them out of the Kai Iwi lakes.
Simple actions that help to minimise human impacts on the lakes, such as always checking, cleaning and drying equipment between waterways to avoid spreading pests, were demonstrated by the Department of Conservation, Whitebait Connection and Northland Regional Council.
Grace Christey, 8, signals she's okay in the clear blue water of Lake Taharoa.
There were also live and static displays, and games that showcased the life of the lakes.
The event was organised by the Mountains to Sea Conservation Trust, in conjunction with Northland Regional and Kaipara District councils, the DoC, Te Roroa and the Taharoa Domain Governance Committee, and also supported activity providers, Te Kopuru Volunteer Fire Brigade and Pub Charity.
Event co-ordinator Kim Jones said: "I'm really pleased with how the day went - despite the rain, we still had a good turnout and received fantastic feedback, now we'll be looking forward, getting feedback from our partners and considering putting on another open day in 2016."