Shark Week episode highlights dead zone killing fish, marine life in Indian River Lagoon

• Bull sharks use the Indian River Lagoon as a nursery.
• Juveniles live in the lagoon for up to 8 years before moving to the ocean.
• A Shark Week crew found one dead and one diseased bull shark.
• Shark biologist blamed nutrient pollution that feeds algae blooms.

When "Shark Week" scientists and film crews explored the Indian River Lagoon for seven days in May, it took them three days just to find one living bull shark to which they could attach a sensor to monitor water quality.

Bull sharks are supposed to be common in the 156-mile-long lagoon, so shark biologist Craig O’Connell was surprised to find a dead zone with dead fish and dead and diseased sharks in one of North America's most biologically diverse estuaries.

"At first, I had hope," the "Shark Week" presenter said. "I was like, 'These bull sharks can tolerate everything,' and then I saw this dead zone. There was no life, and it made me realize that this is an absolutely massive problem."

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What is a dead zone?

The “Sharks of the Dead Zone” episode, which premieres at 9 p.m. Friday, explores how water pollution and algae blooms can create "eerie dead zones" in the lagoon. They can occur naturally or through human activity, such as nutrient pollution, according to the National Oceanic and Atmospheric Administration.

The lagoon is polluted predominately with nitrogen and phosphorus from sewage, urban and agricultural fertilizers and Lake Okeechobee discharges. Coupled with warming waters, they can feed algae blooms.

"The algal growth increases more and more to the point where you get this absolutely massive algal bloom that leads to this dead zone," O'Connell said. "All the oxygen gets sucked out of the water and nothing can survive."

Bull sharks, one of the few shark species that can live in freshwater, use thelagoon as a nursery. Juveniles can spend up to eight years there, before moving to the ocean, TCPalm previously has reported.

The "Shark Week" crew came across only two juvenile bull sharks: one dead with no signs of predation and one alive with its fins and reproductive organs covered in abnormal growths. O'Connell concluded the lagoon's environment negatively affected them.

"I am a little bit fearful for the future of the Indian River Lagoon unless we change our ways," he said.

When is Shark Week 2024?

"Shark Week" runs from July 7-13 and consists of 21 one-hour episodes that air on the Discovery Channel starting at 8 p.m. every night. You can also stream them on Max. Here's the complete Shark Week schedule.

The host of "Shark Week," now in its 36th year, is John Cena, an actor, producer and former professional wrestler.

Gianna Montesano is TCPalm’s trending reporter. You can contact her at gianna.montesano@tcpalm.com, 772-409-1429, or follow her on X (formerly Twitter) @gonthescene.