@SPARKY1922 I think I've got it. It is just that the number I used isn't correct yet but I'm over it for today.
I started a fresh game with a fresh sim that I turned into a mermaid.
I made a dive lot and didn't decorate it and there was no routing fail.
I made a second dive lot and decorated it and saved it to my library.
All would be good at this point except the mermaids did that jump into the sky when approaching the lot.
So - here's where the trouble started.
1. I went into Edit Town
2. Turned on Cheats ....
3. ConstrainFloorElevation False
4. EnableLotLocking On
5. SetImportedTerrainOffset -0.3 (This number turned out to be too much and the bouy is sunk to half way up the flag pole - will try again one day with a smaller n umber - maybe -0.03
6. BuyDebug On - probably not necessary as everything was already on the lot
7. I did not bulldoze the existing lot - doing this causes massive problems - I found out the hard way
8. I simply placed the dive lot from the library onto the existing lot
9. The existing lot had all the dive decor poking up and it'd been made No Visitors Allowed
10. I changed the lot type to Diving Area
11. Saved with a new file name
12. Shut it down
13. Reopened the Save
14. It all looked good
15. Mermaid swam and didn't jump up into the sky but the dive buoy is too low in the water so I'll have to try again with the lower number as mentioned above
16. While mermaid was swimming in the dive lot another mermaid turned up. It seems the game turned one of the townies into a mermaid to come and visit her.
I think that's it.
There was about another 20 steps before I got it decorated and will let you know that later as I have to get ready to go out again now.
Dive lots placed here - probably can't see them but they are there
undecorated dive lot can just be made out by the squareish change in colour of the sea. I looked for deeper parts of the ocean to place the dive lots and didn't need to dig down to make them deep enough.
https://s5.postimg.org/kgdgrdn6v/STDive012.jpg
Other,
- two dark smudges are the two mermaids in the dive lot
https://s5.postimg.org/4uw57f3iv/STDive011.jpg
She went down and I realised she is wearing her sunglasses - I got them off eventually.
https://s5.postimg.org/es760idpj/STDive010.jpg
Just a pretty Sunlit Tides sunset
https://s5.postimg.org/wi8ulj453/STDive009.jpg
https://s5.postimg.org/vfyo313c7/STDive008.jpg
https://s5.postimg.org/5x6bq0c2f/STDive007.jpg
Used Master Controller to take her into Stylist to remove the sunnies - only way to get them off when they are wearing their tail. Much trial and error has proved that for me.
https://s5.postimg.org/7ozakvsuf/STDive006.jpg
https://s5.postimg.org/rwcqd6y1j/STDive005.jpg
Just swimming around - didn't look for spawning fish.
https://s5.postimg.org/57njdotjb/STDive004.jpg
Shock - what's that? A second mermaid - but I only have one in the world
https://s5.postimg.org/45dcv4vaf/STDive003.jpg
He seems friendly
https://s5.postimg.org/69xpw7hhj/STDive002.jpg
https://s5.postimg.org/a6b1s7a6v/STDive001.jpg
Gotta go.
But it can be done - and they can be stopped from leaping into the air as they cross over the boundary but that takes a lot of determination to make that particular work around work.
NOTE - the sea grass is there and green. Don't know why it didn't work before - maybe I was looking at it from too far away as it does change colour and vanish into the distance. The only parts I dug down in this dive lot was where you see the sea floor isn't flat.
Also - those mermaids made pink hearts.
And one more thing - the myth that you can't have dive lots in Sunlit Tides - BUSTED. ;)
Of course, it remains to be seen if she can use it again on another day.... But I'll worry about that tomorrow.