I have been recently thinking about how the water level of Lake Mead keeps dropping due to its high water evaporation rate brought on by recent years of historical drought conditions. The continuous lowering of Lake Mead threatens to shut down Hoover Dam and also threatens the water supply for Las Vegas, since they get most of their drinking water from Lake Mead.

As a short term solution to this problem, I am thinking that it might be worthwhile for the U.S. Army Corps of Engineers to start laying down long sheets of bubble wrap over the surface of Lake Mead to reduce the rate of water evaporation. Large quantities of water vapor would be trapped beneath the sheets of bubble wrap and this should reduce the amount of water lost to evaporation.

I am sure large amounts of bubble wrap could be quickly manufactured especially if the U.S. government were to subsidize bubble wrap manufacturers around the nation, and if they also were to pay for the transport of this bubble wrap from these factories to Lake Mead. The U.S government could also pay for the costs of ships and crews deploying the bubble wrap out on the lake.

Lake Mead is 247 square miles in size and it may be too expensive to cover all of its surface with sheets of bubble wrap. Yet, even if say only 33% of the lake's surface could be covered, this should still have a significant impact on reducing the amount of water lost to evaporation.

Once the drought comes to an end and the water level on Lake Mead has risen back to its normal level, then these ships would go back out on the lake to collect the bubble wrap and it could be stored in warehouses for future use if the need for it arise again.

Would covering part of Lake Mead with large sheets of bubble wrap reduce the amount of water lost to evaporation?

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    $\begingroup$ Covering the water would stop or slow evaporation . But what about unexpected consequences. I cover my pond in winter with styafoam panels. When my son visits with his dog the first thing the dog does is try to walk on the foam panels and fall into the pond. I expect some wildlife would behave similarly. Only one consequence of how many ? $\endgroup$ May 15 at 16:58
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    $\begingroup$ I'd argue that the human water consumption has a more severe impact on the lake's waterlevel than evaporation. $\endgroup$
    – Erik
    May 16 at 8:04
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    $\begingroup$ There's also the thought that if significant amounts of evaporation could be reduced over a large body of water... there's the potential argument from other communities that see more droughts that they may be getting less rain because of lower moisture levels in the atmosphere. Other weather modification has spurred quite a few lawsuits through the years, and it doesn't appear everything is settled, particularly on the water rights side of things $\endgroup$ May 17 at 4:51
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    $\begingroup$ @JeopardyTempest, that's an interesting point you bring up. It makes me wonder now if the creation of Lake Mead had altered the historical weather patterns in northern Arizona and southern Utah. $\endgroup$
    – user57467
    May 17 at 12:10
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    $\begingroup$ That's an interesting point you remind too, that decreasing evaporation would just be returning towards the historical values. That would quash lawsuits in such a situation? As to how such largescale hydrological engineering impact climate... it's as always a complex and nuanced topic a real challenge to predict or verify (it's hard enough to explain why any particular area has the exact weather it has, nonetheless to explain with confidence what changes something like Lake Mead truly has!) If nothing else, would expect the dewpoint is slightly higher downwind. $\endgroup$ May 17 at 18:34

2 Answers 2


Something similar has been done with plastic balls. I'd guess they're much easier to manufacture, since it doesn't have to be a continuous sheet. It sounds like there is some local water savings, and the time to outweigh the manufacturing water use isn't a huge concern in this context.

Edit: that's evidently not why they have the balls there, but they do say it can reduce evaporation by 85-90% nevertheless.

That being said, I'm not sure what the cost vs benefit would look like. The highest possible value--likely much higher than realistic--for reduced evaporation would be about one-seventh of a very low estimate of the inflow. The losses are dominated by actual use, not evaporation.

  • Discharge from a Colorado River gauge not far upstream of Lake Mead seems to typically be in the range of 10,000-15,000 cfs (about 280 cm at the low end). Not accounting for any inflows between that gauge and Lake Mead, so that's a doubly low estimate.
  • Mean annual potential evapotranspiration from Water Years 2010-2019 (from here) at Lake Mead seems to be about 2 m. If the lake's evaporation was exactly equal to that maximum, and all of it was stopped by the covering, then this would equate to about 40 cm, on average. (That's a remote sensing estimate, so I'm not sure how accurate it is over a large water body; I know some algorithms struggle with that.)
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    $\begingroup$ The You Tube video Why Are 96,000,000 Black Balls on This Reservoir? contradicts why the LA reservoir has black balls on it. "Saving water" may be a convenient media story, but it was more to with preventing the formation of bromate, which is carcinogenic, in the water. As the video explains, bromine naturally occurs in water & is harmless, & it is virtually impossible to remove. However, the reservoir is treated with chlorine, to kill pathogens. Unfortunately bromine + chlorine + UV sun light leads to the production of bromate. ... $\endgroup$
    – Fred
    May 18 at 3:41
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    $\begingroup$ ... They need to use chlorine & they can't remove the bromine, so to prevent the formation of bromate they removed the UV sun light by covering the reservoir with black balls. As the video also states, the black balls were originally marketed as "bird balls" to prevent birds for settling on reservoirs & fouling the water. $\endgroup$
    – Fred
    May 18 at 3:43
  • $\begingroup$ Good point. Looks like the article I linked actually said that as well, but they also do dramatically reduce evaporation. $\endgroup$
    – damp_civil
    May 19 at 15:59
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    $\begingroup$ it is important the balls are opaque, if they let the light through they loose much of the effect. $\endgroup$
    – John
    May 20 at 20:47

Evaporation requires energy (~680 kWh / m³ water) and as always this is mainly supplied by the sun. At Lake Mead I estimate ~ 2000 kWh/m² per year of incoming solar radiation.

A highly reflective bubble wrap (e.g. rescue foil on the top) would be a major improvement. Black shadow balls should therefore actually be white in order to keep the water optimally cool. Funny that the inventor's name is Brian White and that albedo and climate science are foreign words to him. (The idea came from now-retired LADWP biologist Brian White).

But what happens to the bubble wrap in strong winds, waves or hail? Or when a drunken sailor with a motorboat loses his bearings in a dark and foggy night?

There is so much plastic floating in the seas, rivers and lakes that I have an aversion to both solutions for that reason alone. The better solution is therefore imho floating PV-(T), which are easy to install and maintain in smaller plots.

And because solar cells become less efficient as they heat up, the water's cooling effect can increase their conversion ability by as much as 20 percent - Putting Solar Panels on Water Is a Great Idea—but Will It Float?

If you look at such a floating construction (see photos in the link) energetically, each m² of photovoltaic module cools the lake by ~2000KWh and, with an optimized construction, can also offer relatively good wind and evaporation protection for the water surface under the raft.

The annual electricity production of ~ 500 kWh/m² means up to 0.5 TWh/y on a 1 km² PV systems and an estimated 1.5 million m³ of water that does not evaporate and can additionally rush through the turbines of the Hover Dam.

  • Since there are certainly hours when the power station has to hold current peaks on a sunny day, although not so much water would be needed downstream. Those are the times when solar power turns into water saving and 1 km² PV modules with max. ~ 250 MW output can replace a turbine with 100 m³/sec throughput at midday. 100 such hours/y gigantic 36 million m³ can possibly be retained in the lake. 10% of Lake Mead (64km²) covered can thus reduce at least 100-150 million m³ of evaporation & discharge.

While that's only a ~20 cm gain/yr in water level of Lake Mead, if other lakes like Lake Powell upstream and downstream in the Colorado River catchment practice the same policy, this can save many of the water bodies threatened by drying up from catastrophe.This could and must be combined with other policies such as:

  • Save water consumption!
  • Replace drinking water with rainwater from the roof
  • in winter, the lake can be cooled with heat pumps and district heating can supply many adjacent consumers with CO2-free heat
  • in summer the lake stays cooler and then supplies the same consumers with cold.

Actually, evaporation is IMHO for the world climate an important, beneficial process for cooling the earth's surface and for cloud formation. We should therefore definitely invest part of the water saving in vegetation and wildlife, which is also under great pressure due to the drought, and also always represents a CO2 store.

How to set up effective protection against drought AND flooding through intelligent water management can be read here:


Thinking globally water retention and an intensification of evaporation and thus cloud formation even has the potential to lower sea level rise and earth temperature. !!!


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