United States
Environmental Protection
Agency
Total Maximum Daily Loads
THSDLs
TMDL at a Glance
Diamond Lake TMDLs- pH and
Dissolved Oxygen
(approved April 2007)
www.deq.state.or.us/wq/tmdh/umpqua.htm
Factors causing impairment
Aesthetics, fishing, and water contact recreation
designated uses impaired due to elevated pH levels
and reduced dissolved oxygen levels from excessive
algal blooms
Sources contributing to impairment
Introduction of the tui chub, an invasive fish species,
resulting in the removal of native aquatic organisms
that typically control algae growth
Restoration options
Tui chub removal and educational efforts to prevent
introduction of invasive species
Stakeholder involvement
Umpqua National Forest, Oregon Department of Fish
and Wildlife, Oregon Department of Environmental
Quality, Partners for Umpqua Watersheds, Oregon
Wildlife Heritage Foundation, Oregon Division of
State Lands, Oregon Department of Agriculture,
Douglas County, PacifiCorp, watershed residents,
local businesses, and several other state and federal
agencies
Status of waternody
Restoration of aquatic life designated use after removal
of tui chub; anticipated attainment of other water
quality standards with potential delisting by 2010
Benefits to stakeholders
Improved water quality, recreational opportunities
(fishing, boating, and swimming), and lake aesthetics,
as well as increased tourism
Restoring Diamond Lake's Water Quality and Trout
Fishery Through Invasive Species Removal and
Education
The introduction of rainbow trout to the naturally fishless Diamond Lake attracted
both wanted and unwanted visitors, resulting in significant changes to the health of the
lake and lake-based recreational tourism. Fishing enthusiasts visiting Diamond
Lake brought an invasive fish species, the tui chub, to use as live trout bait. (Live
bait is illegal in Oregon.) Over time, the exploding tui chub population not only
took its toll on the rainbow trout fishery, but also on the overall water quality of
the lake. The tui chub fed on larger herbivorous zooplankton—the microscopic
organisms in the lake responsible for controlling algae growth—throwing the
lake's nutrient cycling processes off balance. As a result, Diamond Lake suffered
from excessive growth of toxic algae blooms that increased pH levels and reduced
dissolved oxygen (DO) levels. Diamond Lake could no longer support its aquatic
life designated use and was often closed for recreation during summer months due
to potential health risks.
The Oregon Department of Environmental Quality (ODEQ) initiated the
development of a TMDL to help Diamond Lake restore its aquatic life designated
use. The TMDL analysis predicted that removing the tui chub from Diamond Lake
would restore the lake's nutrient cycling processes and support the aquatic life
designated use. Based on the TMDL recommendations, multiple stakeholders from
the federal, state, and local levels collaborated to develop and implement a plan
to remove the tui chub and restore the trout fishery. The biology and chemistry of
Diamond Lake have shown significant improvement due to the removal of the tui
chub. As a result, Diamond Lake is now both fishable and swimmable. Currently,
Diamond Lake is meeting Oregon's water quality standards and ODEQ expects
to remove Diamond Lake from the state's list of impaired waters in the next
assessment cycle in 2010.
How are TMDLs at work in Diamond Lake?
Through the technical analysis, the Diamond Lake pH and DO TMDL provided
stakeholders with a clearer understanding of the external and internal loads
of nutrients affecting the levels of pH, DO, and algal blooms in the lake. The
final TMDL report provided an explanation of how changes to the biological
community found in Diamond Lake due to the tui chub population changed
how efficiently the lake cycled nutrients, resulting in excessive algal blooms. The
computer model tailored to Diamond Lake used in the TMDL analysis estimated
the percentage of tui chub that stakeholders would need to remove from the
What is a total maximum daily load (TMDL)?
It is a study or analysis that calculates the maximum amount of a pollutant that a waterbody can receive and still meet
water quality standards. The TMDL establishes a pollutant budget and then allocates portions of the overall budget to
the pollutant's sources. For more information on TMDLs, visit EPA's website at www.epa.gov/owow/tmdl.
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lake to improve the lake's nutrient cycling and restore
water quality. In addition, the TMDL analysis revealed
that changes in trout stocking densities would also be
necessary to attain water quality standards.
What is the current status of Diamond Lake
as a result of the TMDL process?
In 2005, partners mechanically and chemically removed
approximately 103,000 pounds of tui chub from Diamond
Lake. Monitoring data collected in Diamond Lake after
the removal of the tui chub demonstrate that the lake now
supports its aquatic life designated use. To monitor the
health of Diamond Lake after the removal of the tui chub,
the Oregon Department of Fish and Wildlife (ODFW)
assessed the lake in 2007 and compiled the 2008 Lake
Conditions Index Report. This report uses metrics related
to water chemistry and biology to measure changes in
the lake's condition. The 2008 report states that Diamond
Lake's pH levels are near or below the 8.5 water quality
criteria value and DO levels meet the water quality
criteria appropriate for Diamond Lake on most days. In
addition, the 2008 report states that chlorophyll a values
decreased from a high of 50 ug/L before the rotenone
treatment to less than 10 ug/L (the numeric water quality
criterion associated with aquatic weeds and algae) after
treatment. Figure 1 illustrates the changes in chlorophyll
a values in Diamond Lake before and after tui chub
removal.
Stocked trout health has also improved since the
eradication of the tui chub, according to ODFW
assessment data. Before the removal of the tui chub,
stocked trout had a growth rate and a survival rate of
I I I I
Feb Apr Jun
Oct
Figure 1. Reduction in algal blooms, as represented by chlorophyll a, before
and after chub removal.
nearly zero. During the summer of 2007, stocked trout
grew an average of two inches per month. ODFW states
that trout growth rates are now similar to the growth
rates observed in the 1970s and 1980s—the decades
known as the hey days for fishing in Diamond Lake.
Data from two years after tui chub eradication and
trout restocking have shown signs of water quality
improvements in Diamond Lake. Benthic organisms,
an important food source for mature trout, increased
from less than 25 pounds per acre (Ibs/ac) in 2004—2006
to 200.6 Ibs/ac in 2007 and 168 Ibs/ac in 2008. Before
treatment of Diamond Lake in 2006, the bio-volume of
cyanobacteria was 24,407 cells per milliliter (cells/ml), or
25.7 percent of the bio-volume. Two years after treatment
of the lake, the bio-volume of cyanobacteria decreased to
49 cells/ml or 4.9 percent of the bio-volume. ODEQ will
use this information and other required data inputs to
run the model used in the TMDL analysis to determine
how these decreases translate into annual cyanobacteria
biomass (i.e., kilograms/year) reductions—the numeric
target established in the TMDL. The pH of Diamond Lake
also decreased from 8.5 to less than 7.8 during this two
year period.
How did local stakeholders benefit from the
TMDL process?
Removal of the tui chub from Diamond Lake provided
the lake's natural nutrient cycling processes to regain
its balance. As a result, both water quality and the lake's
biological communities showed improvement. It is
anticipated that these improvements will lead to Diamond
Lake's removal from the state's list of impaired waters in
2010.
In addition to water quality benefits, the restoration of
Diamond Lake has benefitted stakeholders in several
ways. Additional benefits that followed the restoration of
Diamond Lake include:
O Decreased human health risks. Before treatment
of Diamond Lake to remove the tui chub, state
officials closed the lake for recreation during summer
months when the toxic blue-green algae dominated
the lake. Blue-green algae blooms produce toxins
that are harmful to humans and animals. After
implementation, blue-green algae went from the
dominant algae type in Diamond Lake to only a small
percentage of the algal community.
O Revived tourism to boost local economy. Diamond
Lake recreational enthusiasts contribute approximately
$3.5 million to the local economy each year. Restoring
water quality and aquatic communities have helped to
also restore Diamond Lake's reputation as a favorite
destination for trout anglers. According to ODFW,
Diamond Lake-2
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there were 72,085 angler trips in 2007. These trips
generated an estimated $3.76 million in sales and
$2.57 million in labor income in the area (based on the
2006 value of the dollar). The Diamond Lake Resort,
the third largest employer in the area, had a staff of
80 when tourism was suffering most and has since
increased the staff by over 60 percent due to the boost
in lake-based tourism.
O Improved aesthetics. Significant reductions in
nuisance algae occurred and the lake increased
from a visible depth of 10 feet to almost 50 feet after
implementation.
O Increased educational awareness to prevent spread
of invasive species.
It is illegal to use live bait for fishing anywhere in
Oregon. The educational effort for Diamond Lake
reminds visitors of that law through educational
brochures and signage around the lake. In addition,
partners conducted a boater survey to better
understand boaters' habits and perceptions relating
to the spread of invasive species. Educational efforts
remind boaters and recreational enthusiasts of the
simple steps they can take, such as washing boats and
fishing equipment, to avoid giving aquatic hitchhikers
a free ride to Diamond Lake.
"Anyone working in recreation does it for the
satisfaction, not for the money, but it is our
livelihood. When your lake has a problem, you
get involved to find a solution. Getting involved
answered a lot of questions for us about the area.
We found a solution that had a huge ripple effect
both on the lake's ecosystem and on our local
economy."
—Rick Rockholts, Manager
Diamond Lake Resort
For more information on the Diamond Lake TMDL, contact
Paul Heberling, Oregon Department of Environmental Quality
heberling.paul@deq.state.or.us, (541) 440-3338 x224
For more information on the Oregon TMDL Program, visit www.deq.state.or.us/WQ/TMDLs/TMDLs.htm
&ER&
December 2009
EPA841-F-09-002T
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