It would have been nice if the article would have mentioned what the models were made of and what speeds it was launched to.
From the image, the booster is a solid motor with super sonic airfoil stabilizers, so Mach 1.2 to 2?
If that’s the speed regime, then the model is probably steel or stainless steel.
The models closer to the surface are probably pretty corroded from dissolved oxygen close to the lakes surface or destroyed from water and lake bed impact. The ones in deep water may be very much intact and in excellent condition if they survived impact with the water.
What are the chances that, if the launches of those models into the lake were public knowledge, that a team of scuba divers might have already tried to retrieve one?