Fishy Lake is the 2nd World of Ultra and Super Duper Mario Bros.. The levels there are more water-based and have Cheep-Cheeps as a main enemy. Also Princess Peach has located a new castle near Level 2-1 for the vacation.
Level 2-1 - Grass
The first level of World 2. It takes place in front of a castle that the Toads built for Princess Peach, that looks very similar to Peach's Castle. Basic enemies appear here, as well as Puppup's sister enemy Kittkit, who is a faster and weaker version of Puppup. This level also introduces Springs and has Music Blocks as well as a secret Beanstalk. (The power-up here is the Fire Flower.)
Level 2-2 - Water
The first water level and 2nd level of World 2. The power-up in the level, fitting the theme, is the Water Flower. And also the level introduces water enemies such as Cheep-Cheeps, Bloopers, Deep-Cheeps, and Spike-Cheeps.
Level 2-3 - Sky
A sky level taking place above Level 2-2. Most of the level is set on bridges, with leaping Cheep-Cheeps. (And Spike-Cheeps too). Baby Yoshis and Yoshis once again appear. No new enemies are introduced and after the level, the player has to take a pipe across the lake area.
Level 2-4 - Tower
The second Tower in the game, and Pom Pom's at that. Dry Bones, as usual, appear, in addition to the platforms and block mazes that appear throughout the level. Pom Pom's fight is much like her fight in 3D Land, with her boomerang and shell-stomping technique. The Bunny Suit appears inside the tower, but not many towers have this item.
Level 2-5 - Water
A water level featuring the Bubble Baby Yoshi. This level takes place deep underwater, and introduces Spike Eels and has more Spike-Cheeps.
Level 2-6 - Sky
This level takes place high up on a bridge, and has waterfalls. It introduces the Dash Baby Yoshi to the game, helping Mario speed past the level. This level also introduces Stingbies and Coin Coffers and re-features Biddybuds (but mostly Para-Biddybuds).
Level 2-7 - Grass
This is a side-scrolling level on the ground, with enemies such as Pirahna Plants and Venus Fire Traps. Kittkits are in lots of places and the Bunny Suit is featured once again, and there are also Spiked Blocks and Ball and Chains swinging in most places.
Level 2-8 - Airship
The first Airship in the game. It introduces Airship enemies such as Bullet Bills and Monty Moles in manholes, while also introducing another Bunny enemy, the Bunny Bullet Bill (or Bunny Bill). The boss of this Airship is King K. Rool, returning from Donkey Kong Country. He is in a sort of sailor suit and is "the captain of the Airship". After he is defeated, World 3 opens up!
Level 2-S - Desert
The special level of World 2, taking place in a desert. The power-up is an Ice Flower, and the level introduces Pokeys, Sandmaarghs, and Blokkabloks. Since this World is essentually a lake, this level is kind of a "drought in the lake".