Swimsanity!

Use the bomb drone unleash to make this a lot easier. The unleash gets recharged very quickly since you constantly kill those piranha to recharge the meter. The bomb drone kills those bigger piranha with one hit, so it is a giant help. Also, during those chase phases, activate the bomb drone, so it kills those little piranhas really fast. They usually come from just one direction, so the bomb drone focuses its fire to them only, so they die quickly. Like all Adventure-Sanity maps, you need to master the teleport-mechanic or you will get destroyed in seconds. So aim at a direction and use the -button to launch yourself to save yourself. You can use this to avoid any beams, chains etc. in you way too. It is also possible to teleport to the other side of a platform and the enemies can't go through them.

When the biggest masses of enemies are coming near the end of waves, you need to be at your strongest then. So save that drone for those moments, make sure you have plenty of teleports left and use some basic twin stick shmup game tactics to make the enemies chase you from a single direction, not from all over the place. You can leap behind the enemy with the teleport, to make the stream of enemies come from a single direction.

When the final piranha boss loses its shield, don't be near it, it uses a short range launch attack to try to end your days.