What is a clinging jellyfish?

The clinging jellyfish (Gonionemus vertens) is a small, nearly transparent jellyfish about the size of a dime, with more than 60 tentacles. It carries a neurotoxin, and its sting can be more severe than a common sea-nettle sting. It lives in shallow back bays and estuaries, clinging to eelgrass and submerged vegetation, not in the open surf.

Where in New Jersey are clinging jellyfish found?

Monitoring has recorded them most often in back-bay waters such as the Metedeconk River, the Shrewsbury and Navesink Rivers, the Cape May and Wildwood back bays, and parts of Barnegat Bay. They are a late-spring and early-summer animal in shallow, vegetated water up to about four feet deep.

Does this monitoring data tell me a beach is safe?

No. These are point-in-time sample observations, not a live hazard map, and many samples were logged without a count. The absence of a record does not mean clinging jellyfish are absent. Use the data as background and stay cautious around eelgrass in shallow back-bay water in early summer.

Clinging Jellyfish in Island Beach State Park

Occasional detectionsOcean County

Monitoring summary, current as of the 2026 season. This is a record of past samples, not a live conditions report.

The species has been documented in Island Beach State Park, but sparingly: 14 samples out of 138 recorded clinging jellyfish.

By the numbers

samples with clinging jellyfish

sampled, none found

113

sampled, no count recorded

138

total samples (2017–2025)

Largest single count: 11 · most recent detection: 2020

Among the samples with a recorded count, 14 found clinging jellyfish; 113 more samples were logged without a count and are not folded into that figure.

Year by year

'17

'18

'19

'20

'21

'23

'25

jellyfish counted sampled, none found no count recordedSampling effort varies year to year, so bar height reflects how much crews sampled, not risk.

The recorded detections have thinned out in the more recent samples. Sampling effort varies year to year, though, so this is a note about the record, not a verified decline.

When to be careful

This is a warm-water, early-season animal in New Jersey. Fittingly, the largest count logged in Island Beach State Park, 11, came on July 9, 2018.

The species has been found here, so the usual early-season caution applies in shallow, grassy back-bay water — but the record here is light, not heavy. As elsewhere, this is about the bays, not the ocean beaches.

Where these samples were taken

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Scroll to load jellyfish monitoring map

What the clinging jellyfish is, and what to do if you are stung

The animal

About the size of a dime — roughly 1 inch across — and nearly transparent, so it is easy to miss.
Has more than 60 tentacles and carries a neurotoxin; stings can be painful and, for some people, cause symptoms beyond the skin.
Lives in shallow estuaries and back bays, typically in water up to about 4 feet deep, where it clings to eelgrass and submerged vegetation. It is not an open-surf animal.
This is not the common sea nettle; it is much smaller and its sting can hit harder.
In New Jersey it is most often encountered in late spring and early summer, when back-bay water warms toward the low 80s°F.

If you are stung

If you are stung, get out of the water and seek medical care. Reactions to a clinging jellyfish sting can be more severe than a common sea-nettle sting.

For treatment guidance call the NJ Poison Control Center at 1-800-222-1222, or seek emergency care for severe symptoms.

NJ Poison Control: 1-800-222-1222

Towns nearby

Island Beach State Park sits alongside Berkeley and Seaside Park. If you are headed to any of them, the town guides cover the beaches and where to stay.

How to read this page

A note on how to read this page. Each figure comes from individual sample observations collected by Montclair State University, the NJ Department of Environmental Protection, and ReClam the Bay / Save Barnegat Bay between 2017 and 2025. A count reflects what a crew recorded at one spot on one day; many samples were logged without a count, and those are left out of the tallies rather than treated as zero. Areas are grouped from point samples, so boundaries are approximate. Most importantly, the absence of a record is not proof the species is absent. Data current as of the 2026 season.

Source: NJDEP Bureau of GIS / Montclair State University — Clinging Jellyfish Monitoring. NJDEP data layer.

Frequently asked

Have clinging jellyfish been found in Island Beach State Park?: Yes. Clinging jellyfish have been recorded in Island Beach State Park — 14 samples since 2017, most recently in 2020.
Where in the water are clinging jellyfish a concern?: They live in shallow estuaries and back bays, typically in water up to about four feet deep, where they cling to eelgrass and submerged vegetation. They are not found out in the ocean surf.

Other monitored waters

Northern Barnegat Bay

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