Its in a small part of the prologue, but its mainly in Deep Space Drive-in where you switch between walking movement and swimming movement without changing the water level. Ive looked through all the reasonable logic but can't replicate it and if its a material, you don't get it from the level. Im all out of ideas of where to look. anyone know how to do it?

It's most likely done with the (ever-so-powerful) broadcast chip, combined with checkpoints to turn an anti-grav tweaker on or off for each player. Combine that with some animation and movement modifiers (like press X to go faster) and Bob's yer uncle.

You can put an Animation Tweaker on a Broadcast Microchip to duplicate the animation onto a player. Tweak the Broadcast Microchip to sense 'All in Radius', adjust the radius to the desirable size. You add a Controlinator on to the Broadcast Microchip and tweak it to Receive and make it 'Controlled by Nearest Player'. Get a Anti-Gravity Tweaker, set it to: 1. 100% 2. 60% 3. 90%. Place a Advanced Mover and wire it to the Left Stick. Adjust it to Strength: 100% Speed: 7.0. Get some Speed Sensors and tweak to Activation Speed: 0.2, and tweak the Direction to 1. Up only, 2. Down only, 3. Left only, and 4. Right only. Now you have four Speed Sensors. Get four Animation Tweakers and have 1. Swimming Up, 2. Swimming Down, 3. Swimming Left, and 4. Swimming Right. Now wire the respectful Speed Sensor to Animation Tweaker, and Viola! When you go in the radius, you swim!

Also, you can do: All in Contact for radius and use a non-solid material, but at least for me, Impact Sensors don't work on a non-solid material in LBP3.