Once the largest artificially-made lake in the world, at 422 square kilometers Lago Gatún is still a plenty impressive body of water. It was formed by damming the Río Chagres near its mouth, at Gatún, and is an integral part of the Panama Canal. Transiting ships still follow the submerged riverbed of the Chagres, since it’s the deepest part of the lake.

It’s long been a popular spot with boaters, water-skiers, anglers, and even scuba divers. The diving here is unusual, to say the least. A Belgian locomotive and 8 of its 40 train cars, abandoned during construction days, were recently salvaged from the bottom of the lake, and submerged trees and remnants of old towns are still there. Not surprisingly, however, the water is murky and in some places choked with vegetation. Divers find the experience rather spooky.

However, I advise against diving these days. Caimans have always shared the lake with people, but there are a lot more of them now. An acquaintance whose idea of a fun family outing used to be playing catch-and-release with caimans—we’re not talking a wimp here—told me she would not even go water-skiing in the lake today. “It’s infested,” she said. The lake now also has crocodiles.

In other words, stay in the boat. The fishing here is terrific—the peacock bass population, accidentally introduced decades ago, is so out of control anglers are actually encouraged to catch them to restore some kind of ecological balance. It’s not uncommon for an angler who knows the good spots to catch dozens of fish an hour.

A highlight of a Lago Gatún boat trip is a visit to the primate sanctuary scattered among more than a dozen islands in the lake, known collectively as the Islas Tigre and Islas Las Brujas. Here visitors can spot tamarins, spider monkeys, white-faced capuchins, howlers, and night monkeys swinging or peering from trees just a few meters from the boat.

Only visit the sanctuary on a tour led by a responsible naturalist group such as Ancon Expeditions (tel. 269-9414 or 269-9415, fax 264-3713, www.anconexpeditions.com). Do not feed or have any physical contact with the monkeys. All but the night monkeys have been rescued from illegal captivity, and the project is trying to reintroduce them to the wild. The last thing they need is more human contact. Besides, some can be pretty aggressive, so don’t get too close.

Some boat tours of the area include walks through small, forested islands, some of which have spooky ruins from the old Canal Zone days. Douse yourself with insect repellent before exploring them; the mosquitoes can be voracious.