Assessment of ecosystem response to a temporary water level drawdown and subsequent refilling at Topock Marsh, Arizona—July 2011–October 2014

Open-File Report 2016-1195
Prepared in cooperation with the U.S. Fish and Wildlife Service–Region 2–National Wildlife Refuge System, the Havasu National Wildlife Refuge, and the Desert Landscape Conservation Cooperative
By:  and 



Topock Marsh is a 1,637-hectare (4,045-acre) wetland adjacent to the Colorado River near Needles, California, and a main feature of Havasu National Wildlife Refuge (NWR). The U.S. Fish and Wildlife Service, in cooperation with the Bureau of Reclamation, began construction of an infrastructure improvement project in 2010 to increase the efficiency of water use and to help protect the habitats and species found within the Havasu NWR. During construction, normal water delivery from the Colorado River into Topock Marsh through the Inlet Canal was restricted, which resulted in unusually low water elevations  in 2011. The U.S. Geological Survey, commissioned by the U.S. Fish and Wildlife Service, undertook the investigation of the water quality and aquatic flora and fauna during the low water conditions. Subsequently, water elevations in the marsh returned to more normal elevations after the new concrete-lined Fire Break Canal became fully operational in January 2012.

The U.S. Geological Survey made 11 field trips to the Havasu NWR between July 2011 and October 2014 to assess the effects of the temporary low water conditions and the change of inflow location (from the Inlet Canal to the Fire Break Canal) on water quality and aquatic habitat. The following conditions were monitored: water quality, sediment and plant chemistry, phytoplankton, zooplankton, aquatic macro-invertebrates, and emergent and submerged aquatic vegetation (SAV). Water-quality and biota data collected during 2013–14 were then compared with data collected during the 2011–12 low water period.

Once the new Fire Break Canal became operational and Colorado River water flowed regularly into the marsh, concentrations of several water quality parameters decreased (for example, specific conductance, total dissolved solids, turbidity, chlorophyll a, and total and organic nitrogen), and phytoplankton abundance was reduced at the upstream sampling stations (TP-3, TP-2, and TP-6); the water flow pushed water with higher concentrations of these components downstream (measured at TP-8). The upstream sampling locations in 2013–14 had decreased turbidity, therefore more SAV biomass accumulated, especially in shallow areas with water depths of ≤1.0 meter (≤3.3 feet). However, the furthest downstream station had higher turbidity caused by both the suspension of autochthonous sediment and high phytoplankton density and biovolume. This higher turbidity resulted in minimal SAV growth, especially in the deeper water (>1.0 meter [>3.3 feet]). Emergent vegetation not only survived the low water conditions of 2011, but expanded its areal coverage and subsequently thrived in the higher water elevations. 

Overall, no immediate critically negative consequences were detected for aquatic fauna or flora that could be attributd unequivocally to the effect of low water levels. Concentrations of nutrient and trace elements in all water samples were below wildlife toxicity thresholds as established by Arizona Department of Environmental Quality. Three nonnative species were discovered shortly after the Fire Break Canal went into operation. Of the three, gizzard shad (Dorosoma cepedianum) and Eurasian watermilfoil (Myriophyllum spicatum) increased substantially in numbers from 2011–14, but quagga mussels (Dreissena bugensis) did not increase. Future monitoring will determine the long-term impact of the new flow regime

Suggested Citation

Daniels, J.S., and Haegele, J.C., 2017, Assessment of ecosystem response to a temporary water level drawdown and subsequent refilling at Topock Marsh, Arizona—July 2011–October 2014: U.S. Geological Survey Open-File Report 2016–1195, 93 p.,

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Abstract
  • Introduction
  • Site Description
  • Methods
  • Results
  • Discussion
  • Management Relevancy
  • Conclusions
  • Acknowledgments
  • References Cited
  • Appendix 1. Long-Term Water Chemistry Data for Topock Marsh From Late 1983 to Early 2015
  • Appendix 2. Topock Marsh General Fish Surveys and Reports
Publication type Report
Publication Subtype USGS Numbered Series
Title Assessment of ecosystem response to a temporary water level drawdown and subsequent refilling at Topock Marsh, Arizona—July 2011–October 2014
Series title Open-File Report
Series number 2016-1195
DOI 10.3133/ofr20161195
Year Published 2017
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Fort Collins Science Center
Description Report: vi, 92 p.; Appendixes 1-2
Country United States
State Arizona
Other Geospatial Topock Marsh
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details