I don't really place blame with any one thing, but a mix of a bunch of factors. For the boat, they were motoring much closer to the side with the runway, instead of the side further away. Its not technically wrong, but if they were exercising any caution at all would have been farther away and likely out of our glideslope. On our side, we should have checked more deliberately that nothing was in our path. On base, I saw nothing, but the time we were on final I guess the boat had moved and was then in the way of the runway and neither I nor the pilot in command saw it.

Mostly though, I think there just should have been much more regulation given the number of parties operating in the same space.

It seems that an exclusion zone could and should have been established in the vicinity of this approach, but to say that the boat operator was not "exercising any caution at all" is quite a stretch. Boats traveling in channels have a set of regulations to follow, which include keeping to the side when not crossing.