At a time when California was suffering from a record-breaking drought, removing a dam would have seemed counterintuitive. But that’s what happened in 2015 on the Carmel River when the 106ft San Clemente Dam was torn down in the name of public safety and for the benefit of an iconic fish.

Now, two years later, scientists are evaluating just how big an impact the dam removal has had on steelhead trout, which are listed as threatened under the Endangered Species Act. So far, the results are promising.

“Steelhead trout are crafty,” said Tommy Williams, a scientist with the National Oceanic and Atmospheric Administration (NOAA) tasked with surveying the river for their presence. Like many piscine-oriented people, he holds the anadromous species in high regard. An oceangoing version of rainbow trout, steelhead can migrate in their first, second or third year of life, return to their birthplace to mate and can spawn more than once.

Prior to European settlement, steelhead had survived and thrived through California’s countless droughts and wildfires. Yet despite their tenacity, by the early 21st century they were on the verge of disappearing from the landscape.

The razing of the Sam Clemente Dam served a dual purpose. The sediment-choked reservoir blocked access to the ocean for steelhead and the dam was at risk of catastrophic failure due to earthquakes. Rather than face the prospect of a wall of mud, trees and rocks squashing homes located downstream, the decision was made by the dam’s owner, California American Water, in consultation with federal and state agencies, to demolish the decrepit structure, making it the largest dam-removal project in California’s history.

The project began in 2013 when engineers rerouted a half-mile section of the river above the dam. Remnants of the dam were removed and a series of cascading pools were installed to enable oceangoing fish to swim upstream to the tributaries where they spawn.

Prior to demolition, the prognosis for the steelhead residing in the Carmel River was dire.

Historic steelhead runs on the Carmel River used to be around 20,000 but that number had dropped to fewer than 800 by 2015. NOAA scientist Williams, who has conducted steelhead surveys along sections of the river prior to and after the dam’s demolition, compared their decline to a “death by a thousand cuts.” He attributes their losses to the rise of human habitation in California and to the subsequent demand for water to cultivate crops and for use by cities for the sake of economic development. “We’ve pushed them to the razor’s edge by modifying their habitat,” he said.

Monterey County was no exception. The demand for water led to the construction of the San Clemente Dam in 1921. In turn, the dam blocked the Carmel River’s flow, undermining its ability to support steelhead. And for decades, the steelhead had to climb a fish ladder to swim above the dam, a challenging task made even more difficult during times of flood and drought.

After two years, the river is messy and messy is good. Prior to demolition, the structure had not only blocked steelheads’ ability to swim upstream, but also deprived the river of qualities necessary for their survival. Among them, the river lacked the ability to transfer debris downstream. This is a necessary factor in creating the variety of freshwater habitats young fish require to mature, prior to entering the Pacific Ocean.

Post-dam removal, Williams has seen a mix of fish at various stages of development, both above and below the site of the dam, which is a positive sign that steelhead populations are on the rebound. After surveying numerous sites along the river multiple times, “there’s no cause for concern, and reason for optimism,” he said. He’s upbeat, but he will have to withhold his judgment until NOAA issues its final report, due next spring. With the demolition of the dam, the fish counter used to calculate their numbers was also removed. In turn, the steelhead population is harder to calculate, he explained.

However, the river system is coming back to life. “I’m surprised at how fast the river has responded,” Williams said.

The epic winter storms of 2016 helped speed up the recovery process. Large rocks, fallen trees and tons of sediment located above the dam were swept downstream. And in turn, the debris created ample nooks and crannies for fish to dwell in. As a result of the demolition and subsequent flooding, the river is more complex. “We’re seeing a fish habitat consisting of ripples, runs and pools and not just long runs,” he said. This diversity in habitat is beneficial for fish.

The decision to remove the dam came to a head after state officials decided the dam had outlived its usefulness. Engineers determined the structure was seismically unsafe in 1991, and by 2002 it was full of sediment and no longer supplied water to Monterey residents.

Trish Chapman, the regional manager for the California Coastal Commission, said the decision to remove the dam made sense for the residents of Monterey County and for the fish. Now, the river is linked to the beach and in terms of ecological services, “the most important aspect of taking down the dam is that it reestablishes sediment supply, and with sea level rise we need that everywhere,” she said.

California American Water could have retrofitted the structure for $49 million, a stopgap measure as the dam aged and weakened. Instead, they coordinated with state and federal agencies to raise additional funds for habitat restoration with a total estimated cost of $84 million upon completion.

At this point, the river is in the process of redesigning itself and it’s “super-exciting” to observe, Chapman said. In 2017, the river has the building blocks for a healthy ecosystem, sediment flows downstream and steelhead can move upstream. “Honestly, the river can build a far better river than we do. It’s so much more complex,” she said.