I've found a great time-saving glitch regarding the jetski portion of Big Nate Island.

Here is the glitch being demonstrated:

The glitch is very simple to perform. Simply move your mouse off-screen (not focused on Poptropica) to the right (you don't have to hold LMB), and if your jetski is all the way off the screen, the obstacles will spawn to the left of your jetski, rendering you invincible.

You'll still win the race and proceed normally.

Important to note: The tab where you are performing this glitch must be active (not minimized, not in another tab) for it to continue. Another window would work if you wanted to do a run with multiple instances of Poptropica.