Can someone explain the fish that swim in the sand?

My brother and I recently started watching T90 and his hidden cup and honestly I've been waiting for something to scratch my RTS esports itch ever since I lost interest in starcraft! Never thought to check the scene for a game that came out the same year of my brother that I also remember getting in a cereal box (the game not my brother) but better late than never and honestly the game is still a joy to play and now watch.

So we had a few drinks and were watching a game on the map I managed to find out was "El Dorado", we saw that the bases spawned on some light looking sand tiles that had sword fish jumping in and out of it.. the villagers were catching these land-fish with nets for food. We lost the next 5 minutes of game play as we laughed at the absurdness but the chat didn't say a word so we presumed it's common place in AOE!

Now I can't find anything at all anywhere online, including the wiki about this quick sand that supports buildings and people but also has amphibious large fish.. and it's killing me I can't find anyone talking about it or a single entry documenting its absurd existence.

I know this probably seems over the top but a simple google search turned into 2 hours of intensive detective work and turned out nothing and now I've been driven to asking for help; we just wanna know a little more about the sand-fish haha

Thank you in advance