Invasive mussels

Overview

Figure 1. Quagga mussels encrust an access ladder in the Central Arizona Project aqueduct. (Image Source: Central Arizona Project, Aquatic Invasive Species in the CAP)

Quagga Mussels (Dreissena bugensis) are a freshwater mollusk native to Eastern Europe which have become damaging invasive species across much of the United States, including the Colorado River Basin (Figure 2). It is believed that these mussles arrived in the Great Lakes in the late 1980s via ships from Europe that inadvertently carried them in ballast water tanks. Both the mussel adults and larvae (veligers) can also attach themselves to boat hulls, and the transport of recreational boats from a mussel-infested water body to a previously uninfested one appears to have driven the spread of mussels to the Colorado River Basin.

Once established in a new water body, these invasive mussels attach themselves to any available surface by the thousands (Figure 1), encrusting, clogging, and otherwise impairing infrastructure for water supply and hydropower. Invasive mussels also degrade recreational opportunities in infested water bodies and rivers, including the need for time-consuming boat inspections and cleaning. In the process of their filter-feeding, quagga mussels also filter large volumes of water–about 1 liter per day per individual. This disrupts the aquatic food web by decreasing the availability of zooplankton for native species, and increased water clarity–which, counterintuitively, can contribute to proliferation of aquatic weeds. The invasive mussels also outcompete native mussels, and harm other species by attaching to their bodies and crowding them out.

Quagga mussels have some predators in the Colorado River system, such as Redear sunfish, smallmouth bass, and crayfish. These predators offer some measure of biological population control, but also a mechanism for the toxins and microorganisms found in the mussels to move up the food chain and bioaccumulate in larger fish and birds, if not humans.

The monitoring of invasive mussels has ramped up to detect and, ideally, contain their spread. Reclamation collects water samples from water bodies across the western states, including the Colorado River Basin, which are analyzed with microscopy to detect veligers, and with molecular methods to detect the presence of mussels using environmental DNA (eDNA). These monitoring results are collated in the Reclamation RISE database (see below).

Figure 2. Quagga mussel and zebra mussel occurrences in the U.S. as of September 2023. (Image Source: US Geological Survey)

Originally found in the Ukraine, the quagga mussel varies from pea-sized to quarter-sized as an adult. They have variable coloration and can be hard to distinguish from zebra mussels. Quagga mussels were first found in the Colorado River Basin in 2007 in Lake Mead, Lake Mohave, and Lake Havasu. In 2012, quagga mussels were found in Lake Powell. Quagga mussels now live throughout the Colorado River system below Lake Mead, including in the Central Arizona Project and all infrastructure in California receiving raw Colorado River water.

There is much concern about quagga mussels spreading in the Upper Basin beyond Lake Powell. While self-sustaining populations have so far failed to establish, individual mussels have been found in several reservoirs in western Colorado and in and northeastern and southwestern Utah.

Zebra Mussels (Dreissena polymorpha) have been found in the Colorado River Basin in Highline Lake, which is undergoing treatment targeting Zebra Mussels in 2023.

Data and tools

Reclamation RISE Database

Reclamation’s RISE database includes invasive mussel count and monitoring data from reservoirs and river reaches with infestations; enter “mussel” in the search bar.

Additional resources

NPS Glen Canyon Mussel Updates

The Glen Canyon National Recreation Area maintains mussel updates on its website, including current watercraft decontamination strategies and requirements.

Invasive Mussel Collaborative

The Invasive Mussel Collaborative collates ongoing prevention and removal projects across the United States, including several which extend through parts of the Colorado River basin.

U.S. Geological Survey Nonindigenous Aquatic Species Database Quagga Mussels

The Nonindigenous Aquatic Species database, hosted by the USGS, provides reports, spatial data sets, and general information regarding non indigenous aquatic species in the United States, including invasive mussels.