The deep blue waters 20 miles off Islamorada looked more like Lake Atlantic than the ocean on a recent Saturday morning — perfect conditions for free-diving and spearing dolphin, wahoo, or tuna.

But the five-member crew on Santiago Alvarez’s 35-foot Contender open-fisherman took measures to tilt the odds even more in their favor. They brought along several stout conventional fishing rods with trolling lures, along with chunks of chum and a well full of live pinfish.

“You can strike out very easily doing bluewater,” said free diver Manny Menendez of South Miami, citing the necessity for angling precautions.

But far from striking out, the party — all members of South Florida Freedivers, a loosely organized club for breath-hold divers, spearfishers, and underwater photographers — managed to load the boat with 20 mahis up to 35 pounds.

Arriving at a patio-sized sargassum patch in about 1,200 feet of water, Raul Boesel deployed a couple of trolling rods with lures and hooked a small schoolie dolphin. As the fish thrashed around next to the boat, a legion of its aqua/green/yellow compatriots swarmed in.

Boesel tossed some chum in the water and dangled a flashy metallic teaser to keep the fish around while Alvarez, Menendez, and Eddie Coloma, Jr. jumped into the water with their spearguns — large Riffe models with up to three thick rubber bands loading the stainless steel spear shaft. The spears had ‘slip tips’, which when fired, turn on a right angle in the fish’s body to hold it secure. Attached to the guns were reels holding 150 feet of line — except for one gun with no reel and a float line with a life-guard buoy attached to the spear shaft. The buoy creates drag so that a large speared fish can’t free itself or dive to the bottom and the diver can simply pull it in hand over hand.

The spearfishermen gave most of the schoolies a pass because they were too small.

“Just midgets,” Menendez called to Ed Coloma Sr., who was driving the boat.

However, about 50 feet away, 17-year-old Eddie Jr. spied a ‘heavy-lifter’ dolphin hanging back from the rest of the school. He shot it, and swam with it back to the boat — his first speared mahi.

He was roundly congratulated by the rest of the group.

“Santiago gave me a couple of pointers,” he said. “When I watch, I learn.”

With only sub-legal schoolies still in the vicinity, the divers decided to continue running and gunning offshore to look for more weed lines, along with floating debris and telltale frigate birds and sooty terns circling and diving.

A few miles away, they came upon a half-dozen terns hovering over patchy weeds. But instead of jumping into the water, the divers held back while Boesel cast a line baited with a live pinfish beneath the birds. He was rewarded with a mahi more than 25 pounds.

As he struggled with the fleeing fish, Alvarez, Menendez and Eddie Jr. dropped into the water to look for more targets. After a few minutes of searching with no luck, they swam back to the boat. Boesel was still fighting his fish.

Shrugging, Alvarez kicked over to the fish and shot it, shortening the battle considerably.

The rest of the expedition followed a similar pattern — motoring around looking for signs of fish, spearing large schoolies, but catching the largest fish of the day — nearly 35 pounds — on Boesel’s rod and reel.