A version of this story originally published in 2019.
Why does the ocean off the Jersey Shore sometimes look incredibly clear and other times murky?
Videos have been popping up all over social media lately showing turquoise water that’s similar to the Caribbean or the Florida Keys.
We asked a few marine science experts this question and this is what we found.
What causes the change of color?
Beachgoers get excited when the water off the Jersey coast looks tropical. But what makes that water seem so desirable?
It’s simple — less particles like sediment or small plankton, called phytoplankton, according to Josh Kohut, professor of marine and coastal sciences at Rutgers University.
Phytoplankton are single-celled plants that float in the ocean and provide about 40-50% of the atmospheric oxygen we breathe.
“Just like plants on land, the plants in the ocean need sunlight and they need nutrients in order to grow,” said Kohut.
The arrival of spring begins to provide the needed sunlight, and the nutrients come from a couple of different sources — from the deeper water further offshore and humans.
“As that warm water moves offshore it’s replaced by the cold water down deep,” said Kohut, describing a process known as upwelling. And because that deeper water has a lot of nutrients phytoplankton start to grow.
“It’s essentially like spreading Miracle-Gro on your garden.”
Kohut said that once the “Miracle-Gro” comes to the surface, and the sun provides energy, over time the water will get more and more murky as the plankton bloom.
“Whenever there is a plankton bloom, that tends to give it kind of a greenish, yellowish, so somewhere in the blue to green to yellow band of colors,” said Anna Pfeiffer-Herbert, assistant professor of Marine Science at Stockton University.
Different species give off different colors. The color comes from pigments they have in their cells, she said.
“When you get hundreds of thousands and millions of them in one patch of water then that color becomes intense and visible.”
Those turquoise hues that resemble tropical waters you sometimes see off the Jersey coast are caused by plankton blooms.
How humans have an effect
The other source of nutrients comes from humans, and it’s all the runoff from the land.
“Everyone is fertilizing their lawns, all the treatment plants are dumping some nutrients into the water,” said Kohut.
Sandy Hook is very influenced by what the Hudson River is doing. Before the rest of New Jersey snickers at that thought, what dumps out of the Hudson actually goes all the way down the coast.
“If there’s been a lot of rain in the Hudson River watershed — all the way up to upstate New York — for the next month or so you’re going to get fresh water coming out of that river that runs along the coast,” said Kohut.
Kohut explains that the water quality of the Hudson River is getting better, but “in the past, the river water would pick up a lot of goodies as it made its way past New York City.”
“When the Hudson River is running it picks up all those nutrients as well,” he said.
These nutrients also fuel the blooms of phytoplankton.
These blooms are not evenly distributed throughout the water and the intense color will be in a patch that gets spread out by the currents. This may be why the water at one beach is a different color than at another.
“If there is a very widespread bloom you may see similar color along the coast,” said Pfeiffer-Herbert. “But a lot of times part of that patch will be close to the Jersey coastline but not another.”
Sediment plays a role
The other source of murky water along the Jersey coast comes from sediment, which includes sand, silt, mud and clay.
“When you are seeing beaches, some that are more murky looking and some that are less, a lot of that might have to do with how close it is to an inlet and which way that freshwater-influenced water is going when it gets out on to the coast,” said Pfeiffer-Herbert.
Some sediment comes from the rivers — finer-grained silts and clays will stay suspended in the water longer — and gives the water more of a brown and opaque look.
“So the further you get from inlets, the clearer the water will get or the less suspended sediment material will be in the water,” she said.
In warmer waters down in Florida or the Caribbean, there tends to be less nutrients, Pfeiffer-Herbert said.
Another factor is that there is less stirring of the water, which means the deeper water does not restore the nutrients. The Sunshine State also has less river runoff compared to the Garden State where we have several big rivers.
“Just because the water’s clear doesn’t mean that it’s free of other types of pollutants, or just because it looks dirty, conversely, it doesn’t mean that it’s polluted in the sense of being harmful at all,” said Pfeiffer-Herbert.
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Tim Hawk may be reached at thawk@njadvancemedia.com. Follow Tim on Instagram @photog_hawk.
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