Special Topics

Foam on the Lower Colorado River

Some occurrences of surface foam have been observed on Lake Havasu, below Parker Dam, and below Headgate Rock Dam, an irrigation diversion dam, in Parker, Arizona. In December, 2011, a significant amount of foam developed at and down river of Parker Dam. Foam covered parts of the lower dam face and much more occurred south of Headgate Rock Dam, where foam bergs” accumulated across the river for 2-3 days (Figure 1). This amount of foam had not been previously reported, so foam/water samples were collected for a chemical analysis of nutrients. Results showed no unusual concentrations of surfactants, phosphate or dissolved organic carbon. The suspected cause of this event was the turnover of water as Lake Havasu de-stratified from its summer condition. This action significantly disturbed the reservoir bottom releasing organic compounds, including surfactants, that accumulated from many years of decomposing organic matter (plants and other organisms, like quagga mussels). Since foam is mostly air, it does not form until the compounds in the water mix with air, such as flowing over or through a dam. Only minor foam events have since been spotted in localized areas, including parts of Lake Havasu, which has been associated with surface water disturbances from high winds and boat traffic.

Figure 1: Waning stages of foam that earlier covered the water between Headgate Rock Dam (right) and the bridges crossing the Colorado River in Parker, AZ (left).

Foam generation is most common in nutrient rich lakes (known as eutrophic lakes), yet the Colorado River and its reservoirs are generally considered nutrient poor (oligotrophic). The quantity of the form of phosphate needed for aquatic plant or algal growth is somewhat lacking in this waterway. However, since the 2007 discovery of quagga mussels in the Lower Colorado River reservoirs and Lake Havasu in particular, water clarity has improved and explosive aquatic plant growth has been experienced, especially at the reservoir’s southern end. In addition, increased occurrences of blue-green algae (Microcystis) have developed since 2009. Decayed organic compounds from these sources may be providing the necessary ingredients to fuel these types of events. Naturally formed foam is not toxic, but its formation can remove dissolved oxygen from the water, possibly leading to fill kills.