horsetooth reservoir

General Information: Horsetooth Reservoir (1900 acres) provides quality fishing for walleye, smallmouth

bass, and trout. Anglers may also catch white bass, crappie, bluegill, and perch. The lake is open year round

to fishing. For more information visit the park’s website: http://www.co.larimer.co.us/parks/Horsetooth.htm

Location: Larimer County. From I-25, go west on Harmony Road 7 mi. to where it becomes CR 38E at Taft

Hill Road. Continue west 4 more miles on CR 38E to park entrance.

Recreational Management: Larimer County

Fishery Management: Coldwater and coolwater angling

Purchase a Fishing License: http://cpw.state.co.us/buyapply/Pages/Fishing.aspx

Regulations

Walleye regulation: 5 fish

bag limit, no size restriction

Minimum size for small-

mouth is 12”

Statewide bag and posses-

sion limits apply for all

other species

Fishing prohibited in inlet

March 15 - May 31

Entry requires a Larimer

County Parks Pass available

on site

Horsetooth Reservoir

FISH SURVEY AND MANAGEMENT DATA Kurt Davies - Aquatic Biologist (Fort Collins)

[email protected] / 970-472-4396

Amenities

4 Boat Ramps

Swim Beach

Modern Restrooms

RV hook-ups

Tent Camping

Camper Cabins

Hiking Trails

Marina

Picnic Areas

Previous Stocking

2013

Rainbow Trout

Cutthroat Trout

2012

Rainbow Trout

Cuttbow

2011

Rainbow Trout

2010

Rainbow Trout

2009

Splake

Rainbow Trout

Cutthroat Trout

Cuttbow

Mercury Advisory

Some fish in Horsetooth have

been found to have significant

levels of mercury. A consump-

tion advisory is in effect. For

more information go to:

http://www.cdphe.state.co.us/

wq/FishCon/

HorsetoothADVISORY.pdf

Sportfishing Notes

Walleye

Fish rock structures when

water temps are 40-55°F.

Later, fish are scattered but

tube jigs, lindy rigs, triple

ripples, are good choices.

White Bass

Watch for surface activity

in the coves, small fish or

birds on the surface, that

indicate feeding fish below.

Smallmouth Bass

Try rock rip-rap areas with

crayfish imitations.

History Horsetooth Reservior was completed in 1949. It is part of

the Colorado-Big Thompson Project (CBT) transporting water from

the west slope and storing it for east slope use. Water operations are

conducted by the Bureau of Reclamation and the Northern Colorado

Water Conservancy District. Expect large water fluctuations in the

reservoir from seasonal water use.

Horsetooth has been managed for cool and coldwater assem-

blies of fish since the 1950’s. Various proportions of rainbows, cut-

throats, browns, mackinaw and splake have made up the coldwater

assembly over time. Coolwater fish like walleye, smallmouth bass,

white bass, and yellow perch have been stocked historically and now

maintain self-sustaining populations.

Horsetooth has had a very dynamic fishery. A large yellow

perch population provided a great forage for walleye from the filling

of the reservoir until the late 1960’s when the population crashed.

When walleye body condition and growth fell to unacceptable levels

as a result, rainbow smelt were introduced as an alternative forage.

This led to a boom in walleye fishing in the 1980’s and 90’s. The

smelt ended up eating themselves out of house and home, affecting

the recruitment of walleye and other fish. The smelt population sub-

sequently crashed and brought the whole reservoir ecosystem down

with it. Smelt disappeared in 1996 and were not seen again for over

a decade

Efforts in the last decade have been to reestablish a quality

forage base without the potentially detrimental effects that smelt had

on the fishery. Spottail shiners, emerald shiners and gizzard shad

have been successfully introduced and represent a significant com-

ponent of the fishery. Walleye maintain a self-sustaining population

and their body condition and growth have continued to be on the rise

for the last few years.

Smelt began to show up again in our sampling in 2010 and

in the last three years, the population has grown from undetectable to

an estimated 2.5 million in 2013. This has created a very dynamic

fishery that will see significant reservoir-wide changes for many

years. We will be monitoring this and making changes when possi-

ble to promote optimal smallmouth and walleye fisheries.


FISH SURVEY AND MANAGEMENT DATA

Kurt Davies - Aquatic Biologist (Fort Collins)


Management

Emergency Trout Salvage:

In 2012 a large number of trout were put into Horsetooth Reservoir from Watson Hatchery in response

to adverse conditions caused by fires in the Cache la Poudre watershed. While there were no significant ef-

fects on fish in the river, the poor water quality coming into the hatchery with fish at high densities led to

stressful conditions. To avoid a large kill, and the loss of these fish, they were evacuated to the nearest body

of water that could take the numbers. Approximately 72,750 trout weighing 23,100 pounds were moved in

one day to Horsetooth. Horsetooth is not typically stocked with rainbows because we get a very poor return to

anglers, but this emergency measure should lead to a large number of trout being caught over the next few

years. Enjoy it while it lasts.

Rainbow Smelt:

From our standardized sonar sample, the

smelt numbers were similar in both 2011 and

2012 with estimates around 1.5 million. Sam-

pling in 2013 showed a significant bump in the

population up to an estimated 2.5 million. This

suggests that while we have yet to see a massive

exponential rise in the population that we saw in

previous decades, the population may be on the

rise. The graph on the right shows the range of

smelt sizes sampled. The 2012 data is from the

spring and the 2013 from fall samples. Smelt

historically reached over 8 inches (200mm) but

we have yet to see many fish reaching those up-

per age classes.

Gizzard Shad:

Gizzard shad introduction in

Horsetooth appears to be increasing

in success. The population continues

to successfully reproduce and main-

tain a strong presence in the reser-

voir. This is very beneficial, adding

to the diversity of forage in the reser-

voir and helping to avoid a total sys-

tem crash if dependent on only one

forage species. Most of the 2013

samples were small young of the

year fish under one inch in length.





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Horsetooth Combined Sampling

Gizzard Shad Captured

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Length Bin (millimeters)

Horsetooth Rainbow Smelt Gillnet Samples

Length-Frequency 2012 and 2013

2012 2013

Management

Walleye:

Body condition of walleye in Horse-

tooth has been steadily increasing since 2010.

The first graph to the left shows body condi-

tion factor. An average, healthy walleye in

Colorado should have a relative weight (Wr)

of 96. There was a significant decline after

1995 when smelt crashed in the reservoir.

From a low of 79 in 2010, walleye Wr in 2013

has climbed to 91. The vertical bars show the

95% confidence interval for the data each

year, taking into account the number of fish

measured and the variation within the sample.

There seem to be two populations present in

the near-shore electrofishing sample that may

be making use of different forage items. One

still in poor condition, with an average Wr of

82, and one in fantastic condition with an av-

erage Wr of 130. This is why you see such a

large confidence bar and an average of the

electrofishing sample at 107.

In the second graph you can see the

difference that exists in the number of fish

captured by each gear. Walleye numbers still

remain high in 2013. This equaled about 24

walleye/net, which was higher than any other

Colorado lake sampled in 2012. The peak in

the 1990’s was at the height of the smelt

population and the peak in 2004 was immedi-

ately following the draw-down of the reser-

voir.

The last graph shows an average

length for all the walleye caught with each

gear. Each gear has a bias especially toward

smaller and young of the year fish. Only 2

fish from the electrofishing sample were over

12 inches, while 305 fish from gillnets were.

There was reproduction in 2012, but the

young of the year numbers were lower in the

electrofishing sample and offset by an untyp-

ical number of relatively large fish around 400

mm (16 inches).





Management

Walleye:

In addition to improving the condition and numbers of walleye in Horsetooth, the increasing forage

base in the reservoir seems to be allowing the walleye to overcome their previous stunted condition. In

2010, fish over 18” represented less than 0.5% of the population. In 2013 that number has grown to

over 7.5% and looks like it will continue to increase.





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Inches

Horsetooth Walleye Length-Frequency Gillnet

Sampling 2010-2013

2010 2011 2012 2013

Management

(Due to poor water conditions for the sampling effort, the 2011 data is shifted lower than typical)

Smallmouth Bass:

The average temperature in Horsetooth is colder than most comparable lakes in the area because the

water comes through the Colorado-Big Thompson Project pipeline from a very cold Grand Lake. This factor,

coupled with relatively low productivity, limits smallmouth growth to about 2 inches/year. This slow growth

rate makes Horsetooth a poor candidate for trophy smallmouth management. It takes about 6 years for a

smallmouth to reach harvestable size at the protected 12 inch minimum size limit in the reservoir. This limit

allows sufficient age and growth for successful reproduc-

tion. With this regulation, smallmouth bass have no re-

cruitment limitations in Horsetooth. It is unknown at this

point how much the smallmouth will take advantage of

the resurgence of rainbow smelt but the growth rate could

increase if they were able to do so. In recent creel sur-

veys, only 7.5% of all smallmouth caught were harvested,

half falling between 12 inches and 13 inches.

To the right, the representative species, relative com-

position, and length and weight ranges for both gill net

and electrofishing samples are shown. Keep in mind that

these numbers show the extremes of the fish that were

collected during sampling. Zeros on the weight range are

young fish weighing less than 0.1 pounds.





horsetooth reservoir

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