Line a large baking sheet with parchment paper or aluminum foil. Place crushed graham crackers in a small bowl.

Place blue candy melts in a microwave-safe tall mug or deep bowl. Microwave at 50% power for 30 seconds, stir, and repeat in 15-second intervals until completely smooth.

Dip a pretzel rod into the melted blue candy, leaving about 2 inches uncoated at the bottom for a handle. Tap gently to remove excess chocolate.

Immediately sprinkle the crushed graham crackers over the bottom inch of the blue chocolate to create the sand.

While the blue coating is still wet, gently press 3 to 4 Goldfish crackers onto the pretzel, facing upwards.

Drop a few white nonpareil sprinkles around the fish to look like underwater bubbles.

Lay the decorated pretzel flat on the prepared baking sheet. Repeat with remaining pretzels.

Allow the pretzels to set at room temperature for 15-20 minutes until the chocolate is completely hardened before serving or storing.