Hypoxic (330’/100m) Rebreather Training — Eagles Nest Cave (Florida)

I posted a while back about my plans to get my Hypoxic (aka MOD3) Rebreather Training with Dr Mel Clark at Eagles Nest cave in Weeki Wachee Springs Park, Florida. I had taken my Cave CCR class with Mel back in April 2019. She is an excellent instructor – patient, insightful, and demanding. When diving a rebreather to hypoxic depths (especially in a cave), nothing less than perfection is acceptable.

Note: I’ve reversed the order of the dives / dates in this post because I think the Eagles Nest dives are more interesting. We went to Ginnie Springs first for skills practice and then to Eagles Nest for deeper dives but I’m posting Eagles Nest first.

Eagles Nest

Eagles Nest is an “infamous” cave in Florida. Unfortunately, too many people go into the cave unprepared. I did my training with Mel not only because she is an excellent instructor, but also because I trust her completely. When you dive like this, even as a student, you still need to be aware that you are dive buddy (in the truest sense of the word) in case anything goes wrong unexpectedly.

Eagles Nest is a sinkhole in a “godforsaken” area of Florida. I’m honestly not sure how or why anybody found the area or started diving there. I do know that famous diving pioneer and explorer Sheck Exley helped map the cave. Looking from above, you would have NO idea that an amazing cave system exists underneath. The bugs are everywhere and ready to extract their pint of blood as the price of admission. The dirt road has recently been improved but used to be almost as risky as the dive itself. They recently also added an outhouse which is a luxury.

Eagles Nest Sinkhole

Map of the Eagles Nest

Why on Earth would anybody ever want to dive there when at least 10 experienced divers have died in that cave? Probably the same reason Mallory wanted to get to the top of Everest: “Because it’s there.” In fact, Eagles Nest has been nicknamed “the Everest of cave diving.”

Day 1 – Upstream Tunnel practice dives

Our first day of diving at Eagles Nest involved a series of dives that were designed to demonstrate skills associated with decompression diving: deco communications, holding stops, etc. We conducted dives to 140′ and 150′ into the Upstream tunnel with “simulated deco” stops and then a dive to 200′ with “real” deco stops. I also had to conduct a SCR drill with three different gas switches on the 200′ dive. Boy was that fun!

Day 2 – The Pit

The second day of diving involved a “real” dive to demonstrate skills and conduct a full bailout ascent.

My original plan was to go through The Pit restriction and bottom out at 290′ or so. Mel and I planned out that dive and it was pretty daunting. The problem isn’t “just” the depth — the problem was the long swim to get to the restriction and then the need to do a full bailout. From the “Top View” in the diagram above, it doesn’t seem far from the entrance to The Pit — but I can tell you from swimming it that it is a LONG distance. Here is a good video that shows some of the route (they went down the Lockwood Tunnel before you get to the Pit Restriction).

We revised the plan and decided to do the same dive but stop at the top of the restriction. Someday I will go back (perhaps once I’m certified on scooters in a cave) and do the original dive plan. The plan was 13 minutes swimming in and getting to The Pit restriction, full bailout and then 8 minutes swimming back to the line up to the surface and the running our deco plan. For those interested, here is a list of the gasses I had:

  • Diluent: 11/70
  • Deep Bailout: 62 cu ft of 15/68
  • Intermediate Bailout: 74 cu ft of 19/46
  • Rich Bailout: 79 cu ft of Nx32
  • 45 cu ft of Nx60 (staged)
  • 40 cu ft of O2 (staged)

I carried three bailout cylinders and we staged two(Nx60 and O2). Mel had a similar bailout configuration.

Luckily, we had a little extra time to fit in a “fun” dive and Mel was able to shoot some video of me in Eagles Nest. I don’t have any of The Pit itself because we went there during a training dive but I do have some video of me in other parts of the cave.

The geological structure at Eagles Nest is really interesting. The entrance to the system involves dropping down through a “chute” that presumably was the result of water flow back during the ice age. Below is a video of me entering through the chute:

Entering Eagles Nest and staging a bailout tank

It is really hard to describe how big and cavernous Eagles Nest really is. By looking at the graphic, it really doesn’t do it justice. I can tell you that the cave literally swallows up light. I don’t care how big or how bright your light is, at certain points in the dive you can’t see anything but the line you are following and blackness. Below is a clip of me swimming downstream. You can see at certain times when the light is not on me that it is just blackness even with my powerful primary light.

Eagles Nest Downstream

Doing deco at Eagles Nest is relatively “easy” compared to the deco I have done in the ocean: no current! There is a big tree trunk from the lip of the chute up through the 20 foot stop.

Deco stop at Eagles Nest

Ginnie Springs – Devil’s Eye / Ear

We spent two days and four dives refreshing my diving and cave skills in Ginnie Springs cave. Ginnie is a great cave to explore. There are a lot of different sections of the cave and it generally bottoms out around 100 feet so it isn’t too deep. There can be quite an outbound flow so it can be challenging getting into the cave, but rewarding once you are in. Luckily, we had some extra time to do a “fun dive” and Mel filmed a few video clips of me in the cave:

Fighting the flow to get into the cave system
Getting ready to enter “The Lips” section – signaling any outgoing divers
Fighting the flow going through “The Lips”
Getting ready to go through the “Keyhole”


A huge “thanks” and hugs and kisses for my wife. She has supported me in pursuing my crazy passion of technical diving. I really needed my MOD3 certification in order to pursue other dive objectives and she has been supportive even in these crazy times of Covid.

Mel Clark is an amazing instructor. I can’t say enough about her. She demands a lot from her students and will push you to be a better diver. She has a large breadth and depth of experience and will give students a lot of “tips and tricks” that will help improve your diving.

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