Home to more than 3,000 animals, Denver Zoo  has gotten greener in recent years. This has nothing to do with the resident pythons (green tree pythons are known for their vivid emerald color): Sustainability has been front and center at the zoo for more than a decade.

“We’ve really been able to integrate sustainability within operations,” says Blair Neelands, the zoo’s sustainability manager. “We’re not this separate, siloed department, we are within operations, but we still work across the zoo.”

Case in point: In 2020, the zoo set ambitious goals to reduce waste by 90 percent, energy consumption by 25 percent and water usage by 50 percent (compared to 2018 levels) by 2025. As of early 2024, the zoo has made strides in each area and looks to move the needle even more before the finish line next year.

The progress toward near-zero waste was stymied in 2023 by a change in composting policy at A-1 Organics. The Front Range’s only industrial-scale composting facility stopped accepting compostable packaging and paper products due to issues with contamination in the incoming waste streams.

That meant the zoo’s waste diversion rate declined to about 50 percent in 2023 after several years at 60 percent or more.

“We have essentially had to cut a good chunk of our compost from going to a compost facility,” says Neelands. “We’re actively looking at if we can start doing some composting onsite. The other thing is trying to figure out how we can integrate some reusable products.”

However, the zoo’s waste stream is notably unlike a fast-food restaurant’s.

“Thirty percent of all of our waste is actually produced by our elephants,” laughs Neelands. “Our elephants produce about a ton or a ton and a half of compostable material every day, so it hasn’t hit us quite as hard as some other organizations.”

Energy reduction has been more straightforward, with the zoo replacing old pumps with high-efficiency units and rethinking boiler usage to cut campus-wide usage by about 6 percent since 2018.

Neelands says the zoo is taking a building-by-building approach. Tropical Discovery, home to 1,800 animals from 300 species, is the largest structure on the 84-acre campus.

“We’ve seen an overall 30 percent reduction in energy just this past year,” says Neelands. “It’s equipment upgrades and automation that is really making a difference in that building on energy use.

“We know that 25 percent was lofty when we look at such a big campus and an old campus, but if we can make some jumps in the next year or two, it might be looking alright by the time we're at the end of that goal.”


The zoo has cut its water consumption by about 25 percent since 2018 with more efficient cleaning techniques and upgrading water-based habitats. For example, the sea lion exhibit is currently in the midst of an upgrade that will lead to even more savings.

“Some of the work we are doing over there is upgrading the life support system,” says Neelands. “That is the equipment that circulates and cleans water. We have them across the zoo for any of our large pools and the animals that live in those pools.”

The bottom line?

“We expect to see a reduction of about 8 million gallons a year just from that work alone,” she notes. “By the time we reach our goal, that 8 million is more than 10 percent of our usage. That’s huge.”

Other aquatic habitats still have a “dump and fill” system where the water is changed on a daily basis, adds Neelands. Installing life support systems would decrease water usage at the cost of more energy, so the zoo aims to strike a balance.

It’s not unlike the curveball thrown by the changes in compost policy. Neelands says she’s remaining flexible as the zoo looks beyond 2025.

“What are we doing by 2030?” she says. “We’re sort of in the beginning stages of what comes next.”

An intern from Colorado State University’s Impact MBA program produced a greenhouse gas baseline for the zoo in 2023, providing more data for making decisions about composting strategy or installing more life support systems. While the zoo is notably shaded, a solar array on the parking garage is on the drawing board.

“How can we get a little more bold?” muses Neelands. “The mantra the last couple years has been, ‘Let’s fix what's broken.’ Once we get there and we reset, how can we move forward with some of these bigger, bolder projects?”