Lake Tahoe’s clarity declines by 5 feet
The Tahoe Keys, once the largest marsh in the basin, has long been a source of degradation of clarity for Lake Tahoe. Photo/Kathryn Reed
By Kathryn Reed
Lake Tahoe’s clarity took a turn for the worse in 2013, with visibility decreasing by 5 feet.
Data released March 13 show the average annual clarity level for 2013 at 70.1 feet. This breaks a two-year gain. The measurements have been taken continuously since 1968, when the Secchi disk could be seen to a depth of 102.4 feet.
UC Davis researchers use what looks like a white dinner plate to measure clarity by dropping it over the side of a boat at various locations throughout the year to record how far down someone on the boat can see it. The highest value recorded in 2013 was 90 feet and the lowest was 49 feet.
“Clarity in Lake Tahoe largely reflected what we saw in the weather in 2013,” Geoff Schladow, director of the UC Davis Tahoe Environmental Research Center, said in a statement. “At the beginning of the year, clarity was lowered by large stream inflows. At the end of the year, the low inflows resulting from the drought conditions helped to improve clarity.”
Clarity continues to improve in the winter (December-March) and decline in the summer (June-September).
- Lake Tahoe Clarity Readings
- • 2013: 70.1 feet
• 2012: 75.3 feet
• 2011: 68.9 feet
• 2010: 64.4 feet
• 2009: 68.1 feet
• 2008: 69.6 feet
• 2007: 70.1 feet
• 2006: 67.7 feet
• 2005: 72.4 feet
• 2004: 73.6 feet
• 2003: 71.0 feet
• 2002: 78.0 feet
• 2001: 73.6 feet
• 2000: 67.3 feet
– Source: UC Davis
Researchers said the large stream inflows in winter 2012-13 were mainly responsible for the lower values. At 63.8 feet, summer clarity nearly mirrored 2012’s 64.4 feet. Still, summer clarity is trending downward.
Through various programs agencies around the lake are trying to restore clarity to 97.4 feet. Reducing fine sediment from reaching Lake Tahoe is one of the major goals.
Even though the 1997 inaugural environmental summit created the environmental improvement program and more than a billion dollars have flowed to the basin for water quality projects, it wasn’t until 2013 that a regional monitoring program for urban stormwater was initiated in the basin. Urban stormwater runoff is believed to be the major contributor to reduced clarity at the lake.
All of the programs and money spent, though, have nothing to do with the shoreline where most people recreate. It wasn’t until last year that the powers that be decided to make a concerted effort to study the muck that is making swimming at some beaches resemble any lake in the U.S. because of the algae and murkiness.
I can say from personal experience that the Eurasian Milfoil is making an absolute mess of the beaches on South Shore. You can’t get away from the stuff at Pope Beach and it has made it all the way to Baldwin Beach. I do try to use a small fishing net to gather up as much as I can and toss it on the beach, but there has got to be a way to get rid of this weed… right?
Want to fix the clarity of Tahoe? Ban the sand. The road crews throw down an inordinate amount of sand, sodium chloride, and goodness knows what else in that mix on the roads all around the basin. It adds to both airborne particulate matter and contaminated runoff.
BAN THE SAND!
Keep in mind that Funding for TERC’s clarity analyses comes from TRPA.
Gordon is right. It’s interesting that the TRPA press release makes it sound like clarity got better. Amazing that TRPA can issue another press release and make it so. According to Joanne Marchetta:
“Through the seasonal and annual fluctuations, the long-term clarity trend is good news, and it tells us that the investments being made on roadways and properties to infiltrate stormwater are working,” said TRPA executive director Joanne Marchetta. “After years of public and private restoration projects, we have succeeded in halting the decline. We recognize that more is needed to restore the lake to its historic clarity level, and science is showing that it can be done. Together, we can save one of the cleanest, purest lakes in the world.”
Five feet less clarity is a DECLINE. Ten feet less clarity during the winter, when clarity has not be getting worse as quickly as the summer clarity (along our beaches), is a DECLINE. Of course in years the clarity was better, TRPA takes credit. Now, in years it was worse, TRPA talks around it and somehow congratulates themselves for it being better?? Thank you for not just re-printing the ridiculous press release Kae.
Large stream inflows? When did this happen.?
The water clarity is used as a political tool by TRPA to get more government grant money for the TRPA. It has been, and it always will be used this way.
Before we all get too excited over this, if you look at the chart provided by UC Davis on lake clarity on the right, you find that 2012 was an anomaly. The clarity was up 6 feet then.
In the 10 years that I’ve been in Lake Tahoe, the difference is not significant. 2003 shows clarity of 71 feet , 2013 shows 70.1 feet. Not a significant difference.
But yes we need to find solutions to the milfoil, run offs from the streets, and the Tahoe keys basin clarity degradation.
Does this study take into account that the lake level itself is down? Therefore clarity might also be down.
70 feet is not much clearer than 64 feet, which was clarity after the 100 year flood from 1997. But 2013 was the driest year in the past century? If the lake isn’t much clearer during a drought what does that say for all the public and private restoration projects? Who is to say that all of these TRPA water quality mitigation fees are well spent?
I agree with M. Elie Alyeshmerni’s comment. I noticed the same thing.
Those numbers show inconsistency if anything. One theory would be: what we are doing to improve lake clarity is so miniscule it’s having no impact, the lake is just going through it’s normal fluctuations.
I’d like to see the numbers all the way back to 1968 by each year. Could there be a link posted to their report? I’d like to see things such as current weather when data is collected, and other important factors that could have an effect on this number….time of day, rainfall, snowpack, dates taken….etc.
Also, one would think there is better technology to measure clarity by now. Dropping a plate in the water and looking over the side of a boat seems silly.
J&B, you took the words right out of my fingers.
I agree that clarity has more or less stabilized in the last fifteen years, but a five foot loss in 2013 is not an improvement, especially during a multi-year period of low precipitation.
Tahoe resident had a couple of interesting points. The first was the request to look at the readings farther back than 2000. The website, http://tahoe.ucdavis.edu/research/clarity.html, includes not only annual figures, but winter and summer as well. Second was the concern re the use of the Secchi dish to measure clarity. As I understand it, various instruments have been tried, but none to date match the accuracy of the human eye.
This link takes you to the readings:
http://terc.ucdavis.edu/research/SecchiData.pdf
LTN staff
The Secchi disk has been used since the 1860’s to “observe” water clarity thanks to Angelo Secchi. The Secchi disk has a theoretical limit of about 250ft. The record observed clarity is 217ft in the Sargasso Sea in 1972. Crater Lake was measured at 144ft in 1972. And, John LaConte recorded 108ft using a 9.5in dinner plate in Lake Tahoe in the year 1873. It should be noted that LaConte took his measurement well after the Tahoe Timber clearcuts had started in the 1860’s.
No dam in Tahoe City = more clarity, less erosion, more public access to beaches, and most of the milfoil dead.
Lou. And no more Tahoe Keys, Ski Run Marina, most of the Marinas in Tahoe and no more access to Emerald Bay by boat. So, I don’t think getting rid of Fanny Bridge is in the cards.
“No dam in Tahoe City = more clarity, less erosion,”
Source?