A group are carrying masks, snorkels and flippers, wetsuits pulled down to their waists, others are paddling about in blow-up boats or diving near flags bobbing in the sea as we leave the shore on Leigh's famous glass-bottom boat.
As we cruise over the top, the busyness of the bay is replaced by an underwater forest of waving kelp branches under the clean glass panels near our feet. A few super-sized snapper swerve into the clear patches to say hello.
"They're not being friendly, they think we have food," says Alex, who is providing commentary. "If you've been fishing, you'll know this isn't normal behaviour - snapper are not normally following boats around. It's illegal to feed the fish at a nature reserve, but people still do.
"It makes research impossible, not least because the snapper are territorial so have eaten up or chased away the other fish here," says Alex. "There's a misunderstanding about the reserve: it's not a zoo, it's just a natural piece of coastline set aside for research purposes."
Alex is so passionate about conservation that I suddenly feel compelled to sign up for every "save the sea" campaign available. He's the perfect person to put the pretty fish into a wider context for us all. He tells us that if we snorkel in the bay, snapper will follow, hoping for food. If they are hand-fed, they can't differentiate fingers from food, so tend to nibble the end off that as well.
"They send you to the hospital and then to prison," quips one man on the boat.
We cruise around to the north reef, where Alex says the environment is more normal in terms of a nature reserve. We spot little grey sweeps, bright blue maumau, butterfish, chubby silver drummers, leatherjackets, striped moki and a school of parore. There's also agar agar, a fluffy seaweed used in icecream and gummy bears, which captivates the kids on the boat.
"The fish are the least studied here," says Alex. "Scientists are more interested in the seaweed. One scientist spent 36 years studying a 1sq m spot."
Alex shows us where they just found a fishing line. "It's pretty sad to think people still try to fish here," he says, reminding us to tell people off if we see this happening.
More than 200,000 people visit Goat Island marine reserve each year, and it's reassuring to know these boat trips run throughout the year educating as well as entertaining.
• The Inner Island Trip is 30 minutes long and costs $20 adults, $10 children, $55 family pass. The 45-minute Around the Island trip is $25 adults, $13 children, $70 family pass and takes you around the island to see the outer reefs and caves of Goat Island. Bookings recommended. glassbottomboat.co.nz or ph (09) 422 6334.
• Visit the Goat Island Marine Discovery Centre, run by the University of Auckland, Goat Island Rd. Ph (09) 373 7599, ext 83645, goatislandmarine.co.nz
• Stop at Matakana Country Park for a coffee and snack afterwards - there's something for "the spring chickens" at the Speckled Hen Cafe, which has boiled eggs and soldiers or cheerios for the littlest members of the family. That's if you can drag them away from the many playhouses including a pink princess castle, buzzy bee, Nemo or red fire engine, or the farm animals to visit behind the cafe. 1 Omaha Flats Rd, Matakana, matakanacountrypark.co.nz
Danielle Wright was a guest of Ateed.