Since I had made quite a bit of progress the first time, I returned to the original. So now she still needed to catch the three-eyed fish. After reading your post, @Auroraskies, I did a test without mods, but nothing changed. Even after two sim days, the floating trash never appeared.
The first time I ever played in OL, using the collection helper, I found that there is a fishing hot spot in Miner's Park, the playground in the non-technology area in the mountains. It was on dry ground. Using MC's object info, I had learned that it was a dystopian fish spawner. Also using MC, I found that it was the only ITF fish spawner in OL. The floating flowers and trash are from base game spawners, modified along with the other changes. I had considered placing one in my current sim's koi pond at home in the present, to see if she could catch them there, but first I tried to find the spawner in Miner's Park. It was not visible in buy debug. I tried building a basement nearby so I could go down one story, but there was still nothing there. Maybe it was even farther down than one basement level, but I decided not to pursue that further. I think someone who was involved with creating OL made a mistake and never caught it. No surprise there. I've found many mistakes that should have been corrected in EA's worlds.
So while my sim was still in the dystopian future, I made a small pond behind her house and placed the spawner there. First thing in the morning, she caught several three-eyed fish, and has finally made her goal of catching every fish in the game. After she returned home in the present, I placed the spawner in her koi pond temporarily, just to see if it would work anywhere other than in the dystopian future. It did. The utopian fish spawner did too. So in the future, when I have a sim with fishing skill and want them to catch those fish, I'm going to place the spawners in the pond behind Miner's park.