I just finished the swimmer's zoo, and it was frustrating trying to get the guests over to the last island. Took 18 months.
For those who have not seen it, there are several islands, and the only way to get to them is from the swim shacks. The swim shacks are set in place, and the terrain tools are purposely turned off. You can not buy more shacks.
I had the guests directed from the savannah entrance to the deciduous/coniferous island, then to the sand island, then to the rainforest island. Each island saw fewer guests - most would come up to the shack, and just turn around (lots of swimming space). With 771 guests there are still a whole shlew on the starting land, and a good half shlew on the first island. Relatively few made it all the way over. I think next time I will skip the sand island and have them go to the rainforest island. That way they only go swimming twice. Setting the shack price down to $2 didn't help pursuade them! I had enough money to buld from the other direction, and that may have helped finally get some over there.
You won't need many stands for this scenario 2 or 3 should do. One animal show is enough, and you can set the price at $0 - you only need the head count. I may also try it again and try to NOT have the guests so happy and see what happens........