11 Things Divers Find Under Docks That Owners Never Expect

By Ed Brannigan, Marine contractor. Reviewed by Dana Whitcombe, technical reviewer.

Dock & Pier Repair | Boat Lift Installation Early June 2019, Gulf Shores, Alabama. The water was clear enough to see your fins, but the bottom was a mystery. I was doing a final inspection on a new pier I'd built, checking the seal on a pipe that ran under the deck. Six feet down, I grabbed a handful of muck and pulled up a woman's flip-flop. Not a pair. One flip-flop, almost new. That's the kind of thing that tells you what's really happening above the waterline. Over three decades on the Gulf and Atlantic coasts, I've worked on hundreds of private and commercial docks. When you drop under a deck, you see what people lose, what they dump, and what just falls apart. Owners are always surprised to see what's down there, but I've got a list of the usual suspects. So whether you're planning a dock inspection, a repair, or you're just curious what's under that old wooden structure, here are the 11 things I always find — and why they matter.

What to Bring Before You Go Down

Before you start poking around, have a plan. If your dock is in saltwater, you're dealing with zero visibility at certain times of day. Bring a powerful dive light — you'll need it to see anything. A mesh bag is essential to carry junk out. And a short steel hook or pry bar to dislodge things from the mud. Also, leave a line from your dive vest to the surface so you can find your way back if the silt kicks up. Check the tide. It's easier to work at low tide when the water is shallower, but you'll have more time with your eyes open if you time it with slack water to avoid currents. Always dive with a buddy, even if it's a novice. Better yet, use a surface-supplied air system for long jobs — it's more stable and you don't have to worry about burn times. If you're inspecting a dock for damage, look at the pilings first. Marine borers can hollow out a timber from the inside and you can't see it from above. Run your hand along the surface; if it crumbles, you've got problems. That's where the unexpected stuff starts.

The 11 Things You'll Find

1. One flip-flop. Not a pair. It always falls off a foot or a dinghy and sinks. The rubber is usually like new. It's a reminder that the dock is a high-traffic area.
2. A socket wrench. Contractors drop them over the edge, and they land in the muck. If it's a brand name and it hasn't rusted solid, you can return it to the guy who lost it. If it's been down there for a month, it's a fishing hazard.
3. A wallet. I've found three. Two had IDs. You can return those. The saltwater doesn't do as much damage as you'd think if it's been under for days. The cards are often still legible. I take them to the local sheriff's office.
4. A cell phone. They slide out of pockets when people lean over. If it's a waterproof model, it might still work after you dry it. But don't plug it into a charger while it's wet—you'll fry it. Put it in rice for a week, then try. Or just pull the SIM and mail it to the carrier.
5. A lead anchor with chain. It's from a boat that got stuck on the bottom and someone cut the line. It's a problem because it snags other anchors and props. You need to mark that spot with a buoy or haul it up with a boat hook.
6. A mooring cleat torn from the deck rail. The stainless steel bolts sheared off because they were installed wrong. That tells you the dock has a maintenance issue. You can rethread the bolts and put it back, but you need to check the backing plate.
7. A hardened bag of Portland cement. Construction crews leave them on the deck and one rolls off. When it cures underwater, it becomes a boulder. You have to break it up with a sledge or wedge, because it stops sediment from settling and creates a hole that can undermine a piling.
8. A 12-volt marine battery. Someone's deep-cycle battery rolled off the dock. They leak acid. You see the gray mush on the case. You need to get it out without touching the leak, then take it to a battery recycler. It's not just junk; it's a pollution source.
9. A bicycle. I've found two. One was a kid's bike with a bent wheel. The other was an adult mountain bike. Both had wasps living in the frame. If you find one with a serial number, report it to the police; it might be stolen. Otherwise, it's a scrap metal job.
10. A bronze propeller. This is a nice find. Props fall off when the shaft breaks. You can often identify the engine size from the pitch and diameter. A dock owner might want it back because it's worth good scrap money. But check with the local coast guard before selling it—it might be reported.
11. An old glass bottle. Not a beer bottle. I mean a vintage soda bottle or an old milk bottle. People threw them back in the day. They're usually intact because the mud settles over them. It's a piece of local history. Keep it, but rinse it first—there's no telling what's inside.

How to Sort the Treasure from the Trash

Not everything you haul up is worth keeping. Here's my rule of thumb: if it's got a serial number or a name, try to return it. If it's hazardous, like a battery or a can of old paint, dispose of it properly. If it's scrap, recycle it. If it's just a single flip-flop, well, the trash can handles it. When you're working on a dock, make a point to salvage anything that looks like it could cause a hazard. A snagged anchor can be pulled up with a winch. A broken prop might be worth something. And always take a picture of your finds before you move them. You'd be surprised how interested the owner is when you pull up a whole bicycle from their own dock. Finally, remember the real job: you're checking the structure, not just cleaning up the bottom. Every time I dive under a dock, I find something that tells me how the dock was built, used, or abused. That's the valuable part.

Frequently Asked Questions

Is it legal to keep what you find under a dock? If you own the dock or the water is private, it's yours. In public waters, you should report any valuable item to the local law enforcement or marine patrol. I've returned wallets and tools. It's the right thing to do. How often should I have a diver inspect my dock? For saltwater, a full bottom survey every five years is a good baseline. If you have an older dock, or you've had a big storm, do it sooner. You're looking for marine-borer damage, loose connections, and anything that might cause a collapse. Do I need dive training to inspect my own dock? You should be a certified diver, and you need to know how to work in low visibility. I'd never do it alone. A buddy or a commercial diver with surface supply is safer. And never climb under a dock—you can get trapped.