Galapagos Trip Advisor
3. Re: El Niño signals.
Water temperatures drop from a comfortably warm, no wetsuit necessary level in March/April, to fresher in May, to maybe at least a light wetsuit would be nice in June - for those not used to cooler waters (I'm from Canada, I can handle those June waters without a wetsuit). A very strong El Niño will result in warm waters throughout the May - December period, almost too warm for pleasure frankly.
The effects on ecosystems is massive - marine ecosystems suffer - nutrient rich waters become nutrient poor, and all marine life, or species dependent on marine life, suffer a great deal. Conversely, terrestrial ecosystems witness a great explosion of life - birds nest 2-3 times a season instead of only 1, the islands are green - there are even rivers - something unheard of in the Galapagos. Big downpours are more common - but you still have plenty of sun. It's warm, it's very humid.
Visiting Galapagos during an El Niño is a very rare treat. The graphic manifestation of ecosystem disruption by sudden climate change is in your face. I first visited Galapagos on the tail end of the last big El Niño, in July 1998.