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City of Tempe statement: Tempe cares about Town Lake user safety and aesthetics

Post Date:09/26/2014 4:23 PM

The City of Tempe cares about the safety and appearance of Tempe Town Lake and has worked throughout its 15-year history to create a regional destination that continues to bring significant returns on our residents’ investment. The city is proud of Tempe Town Lake and understands its importance to the community.

On Sept. 22, the Arizona Republic ran an opinion piece that was as short on facts as it was brief in words. The editorial was based on inaccurate information and contained unfounded, alarmist implications about public health risks.

Post-storm cleanup
Following the storm of Sept. 7-8, the amount of water and debris that flowed into the lake from other sources was significant. When the overflows stopped going over the western dam, a large amount of debris ended up just east of the western dam. The city said that it would take time to clean up that area and conveyed that the first priority was the area between the east and west buoys, where swimming events were planned. In addition to that focus area, crews worked continuously to clean up the whole lake and today it is very nearly back to its typical state.

It is important to note that the city is learning from the experience of the recent storm, as it was more intense than most of us have experienced anywhere – especially in the Valley. We have looked at our lake cleanup procedures and decided we can make adjustments in the future that will allow us to more quickly remove debris next to the west dam. We are evaluating the amount of resources (equipment and personnel) that would be necessary to respond even quicker in the future to the area near the western dam.

Western dam replacement
After the storms, PCL Construction’s work on the dam project was slowed – and, for a few days, stopped – for two reasons. First, because water was flowing over the dam after the Sept. 7-8 storm and workers cannot work in those conditions. Second, after the flows stopped, crews needed to divert water away from the construction site and let the ground west of the dam dry out before moving equipment back in.

Temporary delays in construction had nothing to do with debris collected east of the western dam and it had nothing to do with water quality. Implying that the two matters are linked is incorrect. Dam replacement workers were still working to the extent possible for most of that time. Similar delays will happen throughout the dam replacement anytime there is a major storm event. Crews are back working nearly at 100 percent capacity this week.

It was inaccurate for the Republic to imply the dam replacement project is somehow in jeopardy. The dam replacement is not behind schedule and the completion date of Dec. 28, 2015 has not changed. Even if the storm had been more severe and pushed completion into 2016, the city’s agreement with Bridgestone allows for delays due to severe weather events.

Special events and water quality
The editorial implied that lake events have been canceled as a result of material near the west dam. A single “splash and dash” event on the evening of Sept. 11 was canceled because the area received more than two-tenths of an inch of rain, triggering the city’s retesting policy. Since it takes 24 hours to get test results back, there would not have been enough time to know definitively if the water quality met full body contact standards. Because Tempe takes lake user safety seriously, we did not proceed with the event.

The Sept. 21 Life Time Tri went on as planned, including a swim portion. Event organizers partnered with the city and were prepared for contingencies if the water quality tests had not been what they were. The event organizers Tempe works with are professionals who understand and share our commitment to safety.

E. coli
The science of managing Town Lake water quality is fairly routine and predictable. When we see elevated levels of E. coli in the water, it is from runoff that comes from the Indian Bend Wash, our streets and from points east in the Salt River. Runoff contains animal waste and other materials; therefore, E. coli is sometimes present. When the levels don’t meet state standards, we don’t allow full body contact events.

In the past, when E. coli levels come back higher than state standards, two things are most effective at bringing levels down significantly and quickly: time and sunlight. These organisms function best in a host – they don’t live long in open water. In fact, the city has never needed to treat Town Lake for E. coli in its 15-year history.

The city manages mosquitos at Town Lake. In areas east and west of the lake, a number of other agencies are involved in controlling mosquitos, including Maricopa County, ADOT, the Salt River Pima-Maricopa Indian Community and others. The city’s longtime water quality management firm traps and tests weekly at locations around the lake, and they have done so since before there was water in Town Lake. They trap and test at 13 locations on both sides of the lake, from the upstream area near Tempe Marketplace to the area west of the western dam.

There are no Town Lake mosquito test results before or since the Sept. 7-8 storm that show either a higher-than-normal level of mosquitos for monsoon season or the presence of West Nile Virus-carrying mosquitos. Town Lake is stocked with fish that would consume mosquito larvae if mosquito eggs were deposited in the lake. To date, no mosquito larvae have been found in the lake during weekly testing of surface water.

Interestingly, the city’s contracted water quality expert reports that mosquito levels at the lake proper are lower than before the lake was created. Any seasonal spikes in mosquito numbers typically happen in the marshy areas of the Salt River bed east and west of the lake. That’s because mosquitos like shallow, still pools with lots of shade. They don’t thrive in deep, largely unshaded, moving lakes with hungry, mosquito-eating fish.

Since the early September storms, Maricopa County reports that it is dealing with a large number of so-called floodwater mosquitos upstream from the lake in the Salt River bed. Those mosquitos are annoying in number but they do not carry West Nile Virus. That said, West Nile Virus is a serious issue and one the city does not take lightly; county-wide there have been 37 confirmed cases of West Nile Virus infections and five deaths so far this year.

Whether there are more mosquitos than normal at Town Lake right now is one issue – again, there aren’t, according to recent city tests. But it’s another matter altogether for the Republic to repeat and validate an unattributed question about whether there are West Nile-carrying mosquitos without first doing some due diligence to check the facts. It is irresponsible to invoke the specter of West Nile Virus to make a point.

As entities concerned above all with public safety, the City of Tempe and its regional partners have worked and will continue to work to address any real future mosquito concerns at or near the lake.

Residents or visitors who have questions or concerns about Town Lake maintenance, water quality or mosquitos are invited to call Water Resources Hydrologist Basil Boyd at 480-350-2603 or

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