Jellyfish don't have a "sleep-wake" cycle like humans, but they are generally most active and closer to the surface during the early morning and late evening (dawn and dusk). This is because many species of jellyfish follow a "diel vertical migration," moving toward the surface to feed on plankton that also rises during these low-light periods. Furthermore, high-value "jellyfish swarms" (or blooms) are often influenced by tides and winds rather than the time of day; an incoming tide can push thousands of jellies toward the beach regardless of the sun's position. A peer-to-peer safety tip for 2026: if you are swimming in tropical waters like the Great Barrier Reef or the Gulf of Mexico, the "light" of the midday sun can actually make it harder to see transparent jellies. Always check with local lifeguards for "Jellyfish Advisories," and remember that even "inactive" jellies washed up on the sand can still deliver a high-intensity sting, as their nematocysts (stinging cells) remain active for several hours after they leave the water.