When the magnitude 6.2 earthquake struck 10 km east of the Poás Volcano on Jan. 8, at least 23 people were killed, most in landslides. Humans, however, were not the only victims.

Thousands of fish in the nearby Sarapiquí River in north-central Costa Rica were killed when mudslides choked the waterway, turning it to a continuous trough of sludge. Researchers fear that the river's entire fish population may have been wiped out.

“For the Sarapiquí River, the earthquake was a catastrophe,” said Ron Coleman, a U.S. researcher from California State University in Sacramento, in an e-mail to The Tico Times. “As far as we can tell, the mud that went into the river choked all the oxygen out of the water and killed all of the fish and likely much of the other aquatic life.”

While the full picture of damage to infrastructure, homes and citizens in the area hit hardest by the quake is now beginning to come into focus, the environmental consequences are still unclear.

The Environment, Energy and Telecommunications Ministry (MINAET) estimated that a total of 550 square kilometers (212 square miles) of terrain, including waterways, were affected in some way by the earthquake.

Rafael Gutiérrez, the director of the Cordillera Volcánica Central Conservation Area, the MINAET office that oversees state protected lands in the quake area, confirmed Coleman's report from the Sarapiquí River.

“The landslides have caused the accumulation of mud that... blocked oxygenation, and the fish have died in extremely large quantities,” Gutiérrez said.

Coleman, who has been researching freshwater fish in the region for 14 years, was in the Caribbean plains the day of the earthquake, but arrived at the banks of the Sarapiquí River the following day.

Locals told Coleman that “the water actually appeared to cease flowing downstream” because of the thickness of mud in the river.

The fish researcher warned that in the short term, the damage to the ecosystem is “severe.” He and other scientists believe that not only are all the fish gone, but also the small organisms they feed on. Larger animals will likely move out of the main river, he said.

Estimating that recovery could take “several years, at least,” Coleman called for patience, and faith in nature.

The good news, he added, is that “the tributaries are in good shape and will rebuild the Sarapiquí system.”

See Friday's print or digital edition of The Tico Times for more a detailed report on the impact of the Jan. 8 earthquake on local fish and wildlife.