Invasive and Other Non-Native 

Species of the Lees Ferry Reach 

of the Colorado River

Mark Anderson and Ken Hyde

Glen Canyon National Recreation Area

National Park Service
Executive Order 13751 (Dec 5, 2016)

Safeguarding the Nation From the 

Impacts of Invasive Species

(e) ‘Invasive species’ means, with regard to a particular 

ecosystem, a non-native organism whose introduction 

causes or is likely to cause economic or environmental 

harm, or harm to human, animal, or plant health.
Smallmouth Bass

Invasive VS. Non-Native/Exotic (NPS MP2006)

Native Not Native / Not Invasive Invasive

• Native Species are everything that has or will occur by natural processes

• Non-native or Exotic species are everything else (and all GMOs)

• Invasive Species are the unwanted or harmful Exotic Species

Rainbow Trout Brown Trout

Green Sunfish

Walleye

Flannelmouth Sucker

Introduced & Managed as Sport Fish
NPS Maintenance of Non Native Species

Exotic or Introduced species can be maintained in a park if they are:

• Closely related to an extirpated species, when the native species can’t 

survive, or

• Used to control another exotic species, or

• Needed to meet a desired condition for a (assuming it won’t spread!)

• cultural landscape, or

• historic resource, or

• Intensive visitor experience

• Used for temporary erosion control, or

• Directed by law (enabling legislation etc.)

Paraphrased from NPS Management Policies 2006 (4.4.4)
Sources of River Aquatic Invasive Species

• Lake Powell

• Wide range of non-native warm water fish present

• New exotic additions possible (grass carp, burbot, rusty crayfish, etc.)

• Many species (including fish) can pass through the dam with some rate of survival

• River Users

• Too few water resource users clean, drain, and dry 

(possible source of Didymo & New Zealand mud snails)

• GRCA

• Brown Trout

• Lake Mead

• No dam for invasives to negotiate, raft traffic may also transport
Overview of Top Invasives

• Quagga Mussels 

• New Zealand Mudsnail

• Whirling Disease 

• Didymo/Rock Snot

• Cold Water Invasive Fish

• Warm & Cool Water Invasive Fish

• Smallmouth Bass

• Walleye

• Striped Bass

• Green Sunfish 
Quagga Mussels (Dreisenna bugensis)

• Introduced into Lake Powell in 2012

• Ecological effects of the lake/river unknown

• Planktonic and microscopic larval stage

• High priority  STATE LAWS, DOI INITIATIVE

CLEAN, DRAIN, DRY Quarantines

Moored vessel movement paperwork

• No management options identified
New Zealand Mudsnail (Potamopyrgus antipodarum)

• Present since ~1995, identified in 2002

• Can reach huge densities, cover substrate

• Impacts expected, but not demonstrated

• Parthenogenic (all genetically identical)

• Has operculum

• Can close off shell and retain moisture

• Survives well out of water & during treatments

• Spread primarily on boots and waders
Whirling Disease (Myxobolus cerebralis)

• Parasite on trout – causes deformities and neurological damage

• Needs secondary host (tubificid worm)

• Detected in 2007 – again (and worse) in 2012

• No Deformities Reported in LF Reach

• Spread in mud on boots and waders

or in live fish or fish parts
Rock Snot (Didymo?)

• Maybe native 

• From North America and Europe (widely spread in 1800s)

• First problems reported in the 1990s (not here)

• Responds to Phosphorus 

• Absorbs P through stalk

• Stalk elongates in low P

• Quagga mussels can accelerate P cycling (Great Lakes)

• Patchy and transient in Lees Ferry Reach

• Rock Snot reported on the courtesy dock was Cymbella

Coke Bottle

Sickle Shape

Didymo

Cymbella
Boot and Wader Cleaning

• Many invasive species are spread on boots and waders

• Facilities exists at the fish cleaning station

• Poorly used location – few know it exists

• Consists of a small sign and a hose with running water

• New boot/wader cleaning stations are coming

• Up to seven are approved

• Convenient locations

• Better messaging
Trout  Rainbow vs. Brown

Comprehensive Fisheries Management Plan

RBT and HBC can peacefully coexist – no need for the traditional battles

With a healthy population structure few RBT go downstream (small HBC threat)

• BT don’t mind the cloudy water as much as RBT (more likely to go downstream)

• BT eat more fish than RBT (potentially more impactful to HBC)

• BT can disrupt RBT populations (BT don’t fit; they may destroy the only thing that does (RBT))

BT are exotic, likely to spread, and to cause harm

BT are invasive!

Ich muss 

ich sein! 

I gotta be me! 

(in German)
Other Invasive Fish

Smallmouth Bass

Great concern to fisheries biologists, exist in Lake Powell, worse than GSF

Walleye

They are in the Lees Ferry Reach but not taking off for unknown reasons

Striped Bass

Exist in Lake Powell, seen in the Lower Slough and caught in Lees Ferry Reach

What else? Everything that has or will get introduced into the upper 

basin has potential to be invasive. 

Already this millennium  Gizzard shad, Grass carp, Bullfrogs, Quagga
Green Sunfish

• From Lake Powell, reproduce in Upper Slough (-12m)

• Could impact HBC if washed down in HFE

• Rotenone, Ammonia x2, Exclusion, Plastic Treatment

• The upper slough is currently GSF Free! Barriers are in place.

• Expanded Non-native Aquatic Species Management Plan - TOOLS
• 2015 – There was a large and multi-aged population of GSF in both sloughs 

when first discovered. They may have been present for years.

• 2016 – GSF were able to get back into the Upper Slough thru the small 

outlet (no 2015 HFE) – it may have only been 2 to 10 GSF.

• 2016 & 2017 – No GSF reproduction has been found in the Lower Slough so 

far. Colder water and daily fluctuations are likely reasons.

Lessons Learned from Upper Slough 2015-17

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1-Jul4-Jul7-Jul

10-Jul12-Jul15-Jul18-Jul21-Jul24-Jul27-Jul29-Jul

1-Aug4-Aug7-Aug

10-Aug13-Aug15-Aug18-Aug21-Aug24-Aug27-Aug30-Aug

1-Sep4-Sep7-Sep

10-Sep13-Sep16-Sep18-Sep21-Sep24-Sep27-Sep30-Sep

3-Oct

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Upper and Lower Slough Temperature

Lower Slough Upper Slough

• 2017 – HOBO temperature monitors show the Upper Slough reaching daily 

temperatures in the mid-80’s for most of the summer
• 2015 – There was a large and multi-aged population of GSF in both sloughs 

when first discovered. They may have been present for years.

• 2016 – GSF were able to get back into the Upper Slough thru the small 

outlet (no 2015 HFE) – it may have only been 2 to 10 GSF.

• 2016 & 2017 – No GSF reproduction has been found in the Lower Slough so 

far. Colder water and daily fluctuations are likely reasons.

• 2017 – HOBO temperature monitors show the Upper Slough reaching daily 

temperatures in the mid-80’s for most of the summer

Lessons Learned from Upper Slough 2015-17

• Exclusion screens appear to work well in all but HFE & Equalization Flows

• Water conductivity data indicate that the Upper Slough is spring fed and 

perched above the river level – this opens up additional options with very 

low take of life should GSF or other invasives get in the slough! 

Upper | Lower  Upper | Lower  Upper | Lower 
Expanded NNAS Plan/EA – Tiered Approach

•Defines Triggers when NPS would go from Tier 1 to 2 

to 3

• Truly Adaptive Management

• Allows NPS to address a number of concerns from the 

Tribes and Public Scoping

• This is ALL DRAFT and Examples do not include all 

Tools

I {' 
Brown Trout as an Example

• Tier 1 – Bounty/Tournament/Angler Education – Use to try to 

maintain Brown Trout at 1%-5% of overall Trout population 

• Trigger - Population heads into 5%-10% range, Rainbow Trout impacts 

are documented, and tagged brown trout are showing up at the LCR

• Tier 2 (+ Tier 1) – Concentrated efforts on spawning beds including 

bed disruption and electrofishing of adults during spawning window

• Trigger - Population exceeds 10% and is impacting rainbow trout 

recruitment, HBC triggers are hit at LCR, and Lees Ferry is identified as 

a primary source of brown trout

• Tier 3 (+Tier 1 & 2) – Electrofishing campaign similar to LCR is initiated 

I {' 
2nd Example – RM -12 Sloughs

• Tier 1 – Exclusion screens are in place between Upper & Lower Slough; 

Monitoring, High-Volume Portable Pumps should any fish be found in Upper 

Slough after next HFE or Equalization flow. 4 hours to pump out, all non-target 

species are electrofished and relocated AND the 2 to 10 green sunfish are 

retained and released into Lake Powell

• Trigger – Other non-native(s) start spawning in Lower Slough

• Tier 2 (+Tier 1) – Isolate Lower Slough with screen/netting, disrupt spawning 

& beds including 1-2 day low flows from Dam (bug flows?), electrofish Lower 

Slough multiple times with all non-targets relocated to river and all Invasives

returned to Lake Powell

I {' 
2nd Example Continued – RM -12 Sloughs

• Trigger – Invasive numbers continue to increase over summer OR the 

Lower Slough becomes a “Hot Spot” for Smallmouth Bass spawning in spite 

of Tier 1 & 2

• Tier 3 (+ Tier 1 & 2) – Rotenone Treatment is necessary for NEW Invasive. 

Longer Term - Do Intensive Tier 2 for coldwater species like Walleye and N. 

Pike – year-round exclusion screens, extensive monitoring, electrofishing 

and removal back to Lake Powell, periodic rotenone treatments on years 

when spawning is just not stopped

• Channelization from River thru both sloughs for cold water delivery ONLY 

works for Smallmouth Bass and Green Sunfish and involves moving an 

estimated 600 to 1,400 cubic yards (60 to 140 dump truck loads) of 

material 

I {' 
Thank you!

Mark Anderson and Ken Hyde

Glen Canyon National Recreation Area

National Park Service

December 23, 1889