Real-Time Flow Rates For The Guadalupe River
The Guadalupe River Real-Time Temperature Monitor
is supported by the generous donations of GRTU Members, Comal County Water
Oriented Recreation District, and Texas Parks and Wildlife
Water Temperature is a critical habitat component of the health of
the trout fishery. Releases of cold, winter-chilled water from the bottom of
Canyon Lake create an artificial cold-water habitat that supports trout
year-round!
To better protect the trout fishery, a "real-time" water temperature monitor has
been placed in the river 7.5 miles below Canyon dam. Hourly read-outs
transmitted to the GRTU website provide accurate, up to the hour water
temperature information.
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How do you protect the trout by monitoring water temperature?
During the warm season, water temperatures below Canyon Dam are highly
dependent on the release rate (measured in cubic feet per second), distance
from the dam, time of day, and even the weather. The water temperature monitor
will give the information needed to plan where and when to fish. When
temperatures warm, trout are subject to stress, so it is best not to fish for
them during those times.
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What are the best water temperatures for trout?
Ideally 57 - 62 degrees. Good temperatures are below 68 degrees. It is widely
accepted by the biologists that temperatures for mortality are 74 to 82
degrees. It doesn't mean that trout will die in 74 degree water, but their
condition could make them susceptible to disease and predators if the
temperature remains high. And catching and playing a trout in this range could
be fatal to the trout, even it it appears to swim away normally. The water
temperature will fluctuate in a 24 hour cycle and usually the water temperature
is highest in the late afternoon. The daily average water temperature is also
important indicator of the conditions in the trout fishery. Trout biologists
believe that the average temperature should be below 72 degrees.
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Why does the Temperature Chart Line of the graph change colors?The
temperature line will change colors according to the amount of stress the trout
are likely to be under which is dependent on the water temperature.
Green is low stress; Yellow is mild stress;
Orange is moderate stress; Red is severe stress.
The colors are calculated using water temperature averaging for the last 3
hours. For mildly stressful conditions, you may wish to use heavier rods, and
bring the trout to release as quickly as possible. It is best to limit fishing
for trout that endure moderate stress to the time of day when temperatures
produce low stress on the trout. For severe stress, to protect the trout, don't
fish in that area!
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OK. Let's say the average temperatue is 67 degrees at the
temperature monitor which indicates good conditions, How far downstream can I
fish and protect trout? Water temperature depends on the
release rate from Canyon Dam, and the season. The following chart shows the
relationship of water release rate and water temperature. The data was
collected over several years by Texas Parks and Wildlife. This represents an
overall average of several summers, and many kinds of conditions. A particular
day may vary several degrees from the overall average.
Average Water Temperature vs Miles downstream of
Canyon Dam
Knowing the most recent average temperature from the Real-Time Water
Temperature Monitor and the flow rate, you can estimate from the curve what
average temperatures are likely to be downstream. Avoid fishing during the time
of day when the peak temperatures are above 72 degrees.
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But I can see water temperatures change throughout the day,
wouldn't it be best to fish when water temperatures are low?.
Yes, indeed. Generally in the mornings, or when the water temperature may be
below 68 degrees, is the best time.
GRTU has negotiated a "Minimum Flow Agreement" with GBRA to provide a sustained
200 cfs flow throughout the warm season. This should protect the trout fishery
for about 11 miles. Without the Flow Agreement, flows normally are higher in
the early summer, but are cut back to 100 cfs later in the summer. You can see
from the chart that most of the river reaches lethal temperatures when flows
are this low!
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