Fix it as it is easy. I drill a hole of about 4mm through base about a 1cm below where base meets bottom of fin. Then insert a brass slug - 4mm wide in hole as a proxy for a 'strengthening pin' which should be 0.5mm less long than base width. Then fill each side with a drop of epoxy. Sand flat. Looks good when dries as brass shines. 2min job excluding time for epoxy to dry.

Nup, that's a heavy stress fracture, probably caused by a lot of sideways load on the fin, it can't get a lot worse, because the finbox should stop it opening up any more. But just gluing the crack, won't be strong enough to resist the kind of loads that cracked it in the first place. The brass dowle also wont help with the sideways loads, but could stop a blow to the rear of the fin making it any worse. Personally I think I'd either ignore it. Or grind it out and replace with lots of fibre.

As an instructor, and as a guy who has had long swims from broken fins, I would say, toss it and get a new one. Don't chance it. Not worth it.

The actual fin extends down into the head and probably isn't cracked. The only way to find out is to grind off the head material and then get a new head cast on. Looks to me that the crack has started where the head material hasn't bonded to the fin properly. I have found this on a few fins I have re boxed when grinding the head down. When the head material gets thin you can get your finger nail under it and peel it off.
Agree, don't use until fixed.
Ask around, there may be someone local that can re box it for you.

segler said..
As an instructor, and as a guy who has had long swims from broken fins, I would say, toss it and get a new one. Don't chance it. Not worth it.

Depends on what you're doing. 2km runs out in the ocean- Totally agree.