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Big Thompson Poised for a Comeback

Blog by: Ben Swigle 12/4/2013

In many ways, the Big Thompson Canyon is representative of Colorado’s signature landscape in the short 30-mile trip between Loveland and Estes Park.  Highway 34 gains 2400 feet of elevation where the rolling hills at the canyon mouth are supplanted by steep canyon walls carved out by the Big Thompson River.  For Estes Park residents, millions of National Park visitors and wildlife enthusiasts, the drive up the newly-reopened Highway 34 has certainly changed but some familiar faces and amenities remain intact.

Recognizable canyon symbols including Indian Village souvenir shop, The Forks State Wildlife Area, and the Viestenz-Smith Mountain Park were essentially wiped out and the Idlewilde Dam is currently being removed.  However, a number of Big Thompson Canyon icons in some sections are essentially unharmed, including one of Colorado’s premier trout fisheries.

Over the past few weeks, Colorado Parks and Wildlife crews have completed electrofishing surveys to assess the status of rainbow and brown trout populations following the flood.  Within the 10-mile catch and release section, which spans the Big Thompson River from Watonia Bridge to the base of Olympus Dam, trout populations were not drastically different from historical numbers and in some cases, populations have actually increased.  In-stream fish habitat within the catch and release section is highly representative of a wild river with numerous deep pools clean of fine sediments containing nests with freshly deposited eggs built by brown trout.

Immediately below Lake Estes, an extremely popular tail-race fishery, post flood surveys estimated this section of river is home to 2,878 adult rainbow and 1,334 brown trout per mile of river.  Compared to the same survey completed in 2011, the number of brown trout is unchanged while the abundance of rainbows more than doubled - a likely result of a flushing effect from Lake Estes. Four miles downstream at the Handicap Fishing Pier-Ramp, total trout abundance measured 4,262 file per mile, a notable increase of roughly 30% (or 950 trout per mile) compared to the 2011 survey.

Below the confluence of the North Fork Big Thomson and The Big Thompson proper near Drake, river habitats have been drastically altered with some sections being artificially channelized - resembling more of an irrigation canal rather than a wild river.  A trout population assessment at Glade Park, near the mouth of the canyon yielded a meager 610 trout per mile, a significant reduction of an approximated 85% (from 4,100 trout per mile) as documented by a 2008 electrofishing survey. 

Immedialy above the Idlewilde Dam trout populations took a hit relative to the 2012 survey that estimated about 4,500 trout per mile; the estimate completed last week yieled only 750 trout per mile.

The silver lining is that all year classes of rainbow and brown trout from 2 – 17 inches were present upstream and should quickly reestablish in depleted sections.  Furthermore, just as highway 34 was reconstructed, so can portions of river devoid of suitable trout habitat.  In the meantime, the catch and release section of the Big Thompson where public access is permitted is currently open to fishing and will produce some quality trout. 

I added some fish photos and some of the raw data including the relative weight data that found the trout are slightly skinny but likely have enough reserves to overwinter.  Most of the fish we handled were quite beautiful.  Get out there!

Credit to original post:

Data immedialy below the dam.A condition factor of 93 is about average. A number of trout are at that level but some individuals are a little skinny.The relative weights for Rainbows in the C&R section.
Big T TroutIdlewilde Dam removalBrown below Olympus
Ram watches during survey.Data from the handicap fishing pier area. 
Blog content © Ben Swigle
Blog Comments
Dubtrout, CO   12/4/2013 3:52:48 PM
Thanks for write up Ben! Did you happen to test anything downstream from Glade Park or thru Loveland? I scouted some sections between Namaqua and FairGrounds Park last weekend. Found some new runs and pools but couldn't seem to locate any fish. Even before the flood this area was a tuff fish with mostly smallish browns. thanks in advance.
Ben Swigle (Swigs), CO   12/4/2013 3:58:07 PM
We efished a site where the Indian Village store used to stand and found very few fish. Same goes for the remains of the Vienstzn-Smith MTN park, not good. I'll probably spend the winter trying my best to figure out how to remedy the situation but not all is lost.
Tiny Stevens, CO   12/4/2013 4:49:47 PM
Great work Ben! Proof positive that nature has a way of taking care of itself sometimes with a little help! Whats the word on St Vrain State Park? Will it re-open soon? Will it be the same multi-species seperated ponds that it once was? Thanks again for the writeup and all of the fine work by the CPW! Tiny
OldMikkDale, CO   12/4/2013 4:59:45 PM
Thanks for the very informative post and the great work you and other do for us sportsmen. I have not fished the Big T before but hope to do so in 14.
Ben Swigle (Swigs), CO   12/4/2013 5:14:53 PM
Here is some info on SVSP
Coyute, CO   12/5/2013 8:28:21 AM
Thanks for the info.
pikeNcolorado, CO   12/5/2013 11:12:40 AM
It's amazing everything those fish went through and they still had great color and were in good condition. Mother Nature at her best.
opencage, CO   12/7/2013 1:09:45 PM
Thanks for the info Ben. Folks interested in helping the clean up along the river in Loveland can visit