(Photo courtesy of Arizona Game and Fish Department)

Quagga mussels attach to hard surfaces like boats and water pipes.

(Photo courtesy of Arizona Game and Fish Department)

Quagga mussels surround a pipe.

An invasive mollusk is a bigger problem for Lake Powell than officials had previously thought.

Officials with the National Park Service in Utah said they have recently detected thousands of adult quagga mussels on canyon walls, the Glen Canyon Dam, boats and other underwater structures. That comes as falling lake levels have exposed surfaces that had previously been underwater.

The Arizona Game and Fish Department said quagga mussels were first found in Arizona in Lake Mead in 2007. One adult can produce up to 1 million larvae per year.

Parks officials said they are focused on keeping the invasive species from spreading to other lakes and rivers. They plan to continue educating people on the spread of mussels and inspecting and decontaminating boats coming in and out of Lake Powell.