When you visit Puerto Rico, one of the must-do things is a trip to one of our bioluminescent bays (or bio-bays). Whether you go to Laguna Grande in Fajardo, Mosquito Bay in Vieques, or La Parguera in Lajas, you’re sure to have an experience that you will never forget.

The health of the biobays is measured by the number of dinoflagellates per unit of water. That measure translates into how "bright" the bay will be. Mosquito Bay is the most healthy. La Parguera is the least healthy. The Department of Natural Resources has taken steps to maintain and improve the health of Laguna Grande.

In any case, the biobay is best experienced on a cloudy or moonless night. While we can’t predict if there will be clouds, we can do a pretty good job of predicting the phase of the moon and the time the moon rises. Those are the main two factors that come into play. In general, it’s best to avoid the 5 to 8 nights prior to the full moon.

The better bio-bay tour operators will be able to tell you in advance if the night you’ve chosen will be a good night, with regard to the phase of the moon and moonrise. Many operators will not even conduct tours on less-than-optimal nights. Others will bring a tarp to use to block out the moonlight.

To help you with your planning, we’re providing the calendar below which indicates the new and full moons, and our opinion of which nights will be better or than others.