There are plenty of places to dive well. This one is different because you do not travel only to see fish: you travel to see a demonstration. What is under the water is the measured result of a specific decision taken by a few families.
01 Seventy-one square kilometres and a reef
The bay is on the east coast of the peninsula's southern end, some hundred kilometres north of the tip. What makes it unusual is the bottom: hard coral colonies on rocky outcrops that run parallel to the coast and sink progressively offshore.
It is the oldest of only three coral reefs on the west coast of North America, reckoned at some twenty thousand years, and the northernmost in the entire eastern Pacific. Within its 71.11 protected square kilometres, eleven coral species have been counted.
It is worth adjusting expectations: this is not the Caribbean. The water is greener, the coral does not form continuous barriers and the underwater landscape is rock with colonies on top. What is spectacular here is not the set, it is the sheer quantity of animals living in it.
02 From 0.75 to 4.24 tonnes per hectare
The park was declared in 1995, after years of overfishing. In 1999, four years on, the scientists measuring fish biomass found no significant difference between this bay and any other area of the gulf: 0.75 tonnes per hectare on average.
By 2009 the figure was 4.24 tonnes per hectare. An absolute increase of 3.49 tonnes, 463 per cent, which remains the largest biomass increase measured in a marine reserve anywhere in the world.
And the breakdown matters more than the total. The biomass of top predators multiplied elevenfold and that of carnivores fourfold: it was not only the small fish that came back, it was the top of the chain, which is the first thing to vanish when a place is overfished.
Four hundred and sixty-three per cent in ten years. They did nothing special: they stopped fishing and they enforced it.
03 Why it worked here and not elsewhere
There are plenty of protected areas on paper in the gulf. This is the only no-take zone that is genuinely enforced, and the explanation the studies themselves give is not technical: it is social.
There was local leadership, cohesion among the village families and effective enforcement. The fishermen who used to live off taking fish out of that bay came to live off showing them to people who come to see them, and that aligned the economic interest with the ban's.
The other half of the explanation is ecological. A bay of this size, with a structured reef and well connected to the rest of the gulf, can repopulate fast once the pressure is lifted. Both conditions had to be met at once.
04 What it is like to get in
The dives are of the accessible kind: rocky bottoms parallel to the coast, getting deeper as you move offshore, and trips in small boats straight off the beach. No technical diving or strong-current experience is needed.
What you will find is quantity. Tight schools that block visibility, groupers that do not move aside, parrotfish working the coral, angelfish and triggerfish everywhere. The feeling is not of rarity, it is of density.
And part of it can be enjoyed without a tank. A good share of the reef is shallow and close to shore, so with a snorkel and mask you already see much of what makes the place famous. It is one of the few spots where snorkelling is not the consolation prize.
05 What the brochures leave out
The first warning is about resources. Protection works, but there are not always enough means to enforce every rule inside the park's boundaries, and those who manage it acknowledge as much.
The second is more uncomfortable, because it includes you. Tourism has brought the village income and made the ban viable, but there is also research warning that rising visitor numbers can damage the ecosystem they come to see. The paradox is real and has no clean solution.
The reasonable thing is to travel knowing it: go with operators from the village itself, touch nothing, chase no animals and accept the limits on numbers and areas when they are set. The experiment is still running and depends on being respected.
06 How to put it together
Two or three full days is plenty, allowing for one to be spoilt by wind. The logical thing is to stay in the village itself, limited as the offer is, because trips leave early and you do not want to depend on an hour's drive.
The best stretch of the year is October to December. The water keeps summer's heat, rain has already dropped to 17.3 millimetres in October and 6.2 in November, and highs come down from 34.0 to 25.5 degrees between October and December.
And there is one month to avoid above the rest: September, with 81.4 millimetres, 44 per cent of the annual rain, and the peak tropical cyclone risk. It is not about getting wet: a system like that cancels whole days at sea.
