Jellyfish Season in Florida Keys for Snorkeling?

By Cary Bennett – (Roswell, GA)
Is there a high jellyfish season in the Florida Keys? I have a snorkeling trip planned for the Middle Keys for late September and thought we were all set, until I did more reading just now and realized that it may well put us in the water during jellyfish season.

Has anyone been there during the September time frame and have any experiences to offer on this front? I am beginning to consider other locations so as not to waste time and resources ($$) if we will be spending all of our time dodging jellies.

I have read reports on TripAdvisor from last September of people getting in the water and encountering so many jellies that they got out and gave up after only a couple of minutes and were upset that they had wasted money without knowing how bad it was going to be. With this being a warmer than normal year, I suspect this year’s jellyfish population could be astronomical.

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Anonymous – Jul 30, 2012 – Jellyfish Horrible on Our Last Trip

We took our first trip for snorkeling the Keys in August, 2011. No one had mentioned the problem of jellyfish until we were in a guided snorkeling boat heading out to the reef area (already had paid and already trapped for the day). The guides said to just swim around them but that there may be quite a few because of the strong winds they had had in the previous week. Winds sometimes carry them in we were told.

The experience was absolutely horrible, at least for newbies to snorkeling. There were so many jellies that you could not avoid them, and at least five of the snorkelers had to be rescued out in the water and were panicked and in pain due to numerous stings. My daughter was trying to get back to the boat and just had to bite the bullet and get stung repeatedly as she swam back. She will never get in the ocean again I am sure.

Most people were only in the water for about 5-10 minutes before they gave up.

An expensive and painful lesson to be sure.

Wisco – Aug 7, 2012 – August Florida Keys Jelly Report

I just got back from the Middle Keys and can report that the jellies are pretty light at Alligator Reef and Sombrero Reef. We saw mostly Moon Jellies of less than six inches in diameter and only ran into a “patch of jellies” during a noon-time snorkel at Alligator. Our guides told us that this year has been better for jellies (fewer of them) compared to 2011.

Bring a small bottle of white vinegar and wear a swim shirt to protect your armpits (the worst place to get stung) and you should be fine. Remember jellies are part of the marine wildlife, so don’t freak out if you see one or happen to get stung.

Jilly M – Feb 9, 2015 – Jelly Season…

While on a ‘girls trip,’ we went snorkeling off Key West. Yes, it was jelly season. (August – September, if I remember.) Yes, I was stung and it hurt a little.

My daughter, however, found out she was allergic. Bring a vinegar solution, and either Benadryl or an antihistamine based sea sickness medicine (which is what I gave her).

Wear a rash guard and long swim tights, if you can. My understanding is that they only sting where they actually touch skin. So cover up and enjoy. Then you don’t need sunscreen so much, either!

Anne W. – Mar 7, 2015 – Jellyfish in the Keys

My husband and I live in North Fort Myers and go over to the Keys throughout the summer, some of the nicest snorkeling with a great variety of fish. The jellyfish are a regular occurrence and you can forget the month of August and most of September. August is horrible, walls and walls of jellyfish. You’ll spend most of your time trying to swim around them or watching out for them.

We like to go in late May to end of July then back out in October and early November before the water cools down too much.

Anelys Pereira – Apr 19, 2015 – Business Owner

Yes, lots of jellyfish in the water in the month of September. Do not go during that time.

Anonymous – Sep 28, 2015 – Jelly Invasion!

We went just recently to Key Largo on a snorkeling tour at John Pennekamp Coral Reef State Park. DO NOT GO in September. There were moon jellyfish everywhere, there was no way around them. Everyone that got off the boat (about 40) managed to get stung. The discomfort lasts about 40 minutes. Save your time and money for the off season.

On a happier note, the short amount of time I was in the water I did get to see some cool fish.

Duluth – Nov 4, 2015 – Looe Key Reef

We arrived in mid-late September for 10 days and were told by locals that the rainy weather was non-stop for the previous two weeks and that the jellyfish were huge purple patches for even longer… We had perfect weather and only found 3-4 individual jellies to take pics of on our snorkeling trip to Looe Key Reef.

On our last day in Florida we snorkeled the beach around Captiva Island and flew out later that day from Fort Myers. Will be visualizing it all winter while I shovel and plow snow.

Amy – Mar 4, 2016 – Jellies

We went on the snorkeling trip in late October 2014. There were jellies, but nothing major. Just make sure and plan your trip on a cloudless day.

Cardy – Apr 16, 2016 – Islamorada Jellies

We took a trip to Islamorada during the end of August beginning of September. There were too many jellies!! There was no way to avoid getting stung.

Tammy – Jul 26, 2016 – Key Largo Jellies

Snorkeled the past three days in various locations. On Molasses Reef and Snappers Ledge there were random clumps of moon jellies floating around and I didn’t get stung at all. French Reef had very few moon jellies and I managed to get zapped twice. It stung quite a bit but after I got back on board the boat and sprayed with vinegar several times, the stinging stopped and I continued snorkeling. Still have some small welts, but pain free. Awesome snorkeling this weekend in spite of my war wounds!

Heidi – Sep 29, 2016 – Jellyfish Middle Keys

We are here last week of September. It rained the first four days then finally a beautiful day, very few jellyfish. It was wonderful. But the next day… if they had been stepping stones, I’d have been able to walk on water.

However, the gulf side had none every day we went out that it didn’t rain.

In past years: August, September, and October have been rough for jellyfish. I think we’re going for June or July from now on, or dive under with a hooka if you can, it works well.

Yanelie – Oct 4, 2016 – Jellyfish Galore

Just got home from mini-vacation in Key Largo 9/30-10/3. We went out on a boat on Saturday to the Christ of the Abyss Statue out of John Pennekamp State Park. We couldn’t even get off the boat, I have never seen so many jellyfish. We were all literally counting them… 25,26… 30,36… incredible. Saturday was a complete disappointment.

We went back out on Sunday to the Mosquito Sandbar to give it another shot. Again, jellies everywhere. Enough was enough, into the water we went. Yes, I know, we are crazy but as Miamians we practically live in the ocean year round. Not much that can keep us away. Apparently, they were all moon jellies that aren’t very dangerous. A few brushed our leg with maybe a little sting, as bad as razor burn, nothing to even say ouch for.

So my advice – do not come in September or October if you prefer not to swim with these pests. Another idea is to wear a wetsuit, that’ll do it. Good luck!

Blue Grass Babies – Jul 16, 2017 – Weekend in the Keys

My girlfriend and I just got back from the Keys. We stayed July 7-10. We went out on three snorkeling trips and did not see one single jelly. BEAUTIFUL weather. Was not too hot. Cloudy from time to time, but that was all.

Anonymous – Aug 25, 2019 – Don’t Go in August

We snorkeled on August 22, 2019, our first day on vacation with a two stop snorkel group. First stop was an artificial reef. There were jellyfish EVERYWHERE. Of the 20 people on the boat, eight were brave enough to get in and four got stung and that was only in 10 minutes. We ended up getting back into the boat and went to the next location, “The Jetties.” There were none in those clear waters close to shore. So that was OK.

I rented a pontoon boat the next day. All over the “darker” areas of the ocean were jellies. Mainly moon jellyfish, cone jellies and a couple of pink bulbous ones I don’t know the name of. All the way up to the outer edge of Crab Island. There weren’t any at Crab Island though. Just in the deeper parts.

Kristin – Sep 14, 2020 – Stung Day Before My September Wedding 2014

My husband and I got married in Key West on Smathers Beach in 2014. The day before my wedding, I was floating in the shallow water, amazed at how buoyant the water made me, when I felt something creep down my arm. As soon as it began shocking me I knew exactly what it was. I ran from the ocean screaming, “IVE BEEN STUNG BY A JELLYFISH!” The only person who believed me was my best friend and maid of honor who offered to urinate on me (ew, no thank you). I ran out, crying like a giant baby and finally went back to my hotel for a shower, an ibuprofen and a nap.

The next day was my wedding and my welts were on the inside of my upper arm, so not terribly noticeable. But I have the pictures and the memories to last me a lifetime!

Don’t go snorkeling in September in the Keys 🙂

ABryan – Sep 19, 2020 – Birthday Bash

We rented a boat and went to Alligator Reef. I’ve been dying to see all the fish right under the lighthouse. The entire boat was amazed of the beautiful water. Right after we anchored we found the waters full of jellyfish.

I was the only one that still decided I had to see what I had come for. They were very thick but I managed to get under the lighthouse. They tend to stay about 1-2 feet from the surface. If you do encounter a wall of them you can go under them.

I stayed in about five minutes and captured some great videos. I do get allergic reactions to be stings so I didn’t want to take my chances. Even though it was a short experience it was still worth it to me. The water is amazing.

The rest of the day we spent at the sandbar. No jellyfish there. So, we learned our lesson September is a bad time to snorkel.

Anonymous – Oct 2, 2020 – Moon Jelly Swarm at Key Largo

On September 9th, I booked a four hour boat snorkel tour out of Pennekamp Park. The day was cloudy and rainy to begin with but visibility was decent enough to see the coral. On my first stop, everything was OK. I was able to enjoy snorkeling above the masses of sea fans.

The second stop was a different story. I was told that this is where you can see Nurse Sharks, Eagle Rays, and maybe a Leatherback Sea Turtle. I was excited to snorkel and was the last one to enter the water. Five seconds in the water, I spotted two giant moon jellies right in front of my face that I totally freaked out and got back on the boat.

I made attempts to go back in the water but I kept seeing more jellies surrounding the boat.

Kelly, Wisconsin – Feb 4, 2021 – January 2021 Jellyfish Stings

We snorkeled at Alligator Reef Lighthouse, from a big boat with 30+ people and three crew members, run by Robbies in Islamorada. It was a gorgeous day with clear water, one foot waves, perfect for snorkeling. The crew captain provided safety info and pointed out a specific type of jellyfish, “Man of War,” we should stay at least 40 feet away from because their sting is powerful and painful.

Before we got the go ahead to get into the water, the captain noticed one of these jellyfish and kept a close eye on it so that no one got too close. Then there was another, and another.

When we were allowed into the water I was the third person in, with my son and niece right behind me. Immediately I felt a sharp zapping sensation to my right wrist, then one on my leg, then on my thigh. The zapping of electric type sensations got more intense as I moved through the water. I immediately voiced my concern to a crew member telling them that something was stinging me over and over asking if they saw anything in the water. She said she didn’t see anything and that I was probably just sensitive to the salt water. Um no definitely not!

Rachel Helgerson – Sep 16, 2022 – Man of War Jellyfish Key West

We just went snorkeling two days ago in Key West. I was shocked when they dropped us in water by live coral reef into a wall of man of war jellyfish. They were everywhere. I’m very surprised that out of 14 of us nobody was stung. I suggest a full body wetsuit.

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