tac13-0838_fig07

F. Bu, bedrock substrate.

A. Qllb, mass of angular shaped, gravel-to-boulder size rock 

material found below a recent terrestrial landslide. 

D. Qgcu, undifferentiated gravel and cobble. E. Qc, cobble and very coarse gravel is dominant substrate. 

B. Qfmg, fine to medium gravel is dominant substrate. C. Qcg, course to very coarse gravel is dominant substrate. 

tac13-0838_fig03

1930 1935 1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 2015

2,045 

2,050 

2,055 

2,060 

2,065 

2,070 

2,075 

Water year

Albeni Falls Dam Completion

Regulation of Lake Pend Oreille

Mean daily water-surface elevation, in feet above NGVD 29

tac13-0838_fig06a

1,860

2,180

2,260

1,780

1,940

2,020

1,820

2,100

2,060

1,900

2,140

1,860

1,820

1,980

2,100

2,140

1,980

2,060

2,060

1,980 2,020

1,900 1,940

1,820

2,220

1,780

1,780

1,820

2,180

2,260

A. Scenic Bay

U.S. Navy 

Acoustic 

Research 

Detachment 

Base

Bayview

Jökulhlaup Point

Cape Horn Peak

116°33'30"W 116°33'W 116°32'30"W 116°32'W

47°

59'N

47°

58'

50"N

47°

58'

40"N

47°

58'

30"N

0 0.1 0.2 0.3 0.4 0.5 MILE

0 0.1 0.2 0.3 0.4 0.5 KILOMETER

N

tac13-0838_fig06b

2,100

1,940

1,820

2,140

2,140

2,060

1,980

2,140

2,100

1,940

1,980

1,820

1,860

1,900

1,940

1,980

2,020

2,060

2,100

1,860

1,900

1,940

1,980

2,020

2,060

2,100

1,820

B. Idlewild Bay

Jökulhlaup Point

47° 47°57'20"N, 116°34'15”W 47°57'25"N 116°34'W 47°57'30"N 116°33'45”W 47°57'35"N 116°33'30”W 47°57'40"N 47°57'45"N 116°33'15”W 47°57'50"N 116°33'W 47°57'55"N 116°32'45”W 47°58'N 47°58'05"N 116°32'30”W

57'

15"N

47°

57'

10"N

47°

57'

05"N

47°

57'

15"N

47°

57'

10"N

47°

57'

05"N

0 0.1 0.2 0.3 0.4 0.5 MILE

0 0.1 0.2 0.3 0.4 0.5 KILOMETER

N

tac13-0838_fig05a

2,100 2,060

2,020

1,980

1,820

2,140

1,860

1,940

2,140

2,220

2,220

2,260

1,780

1,780

1,780

1,940

2,020

1,820

2,060

2,060

1,900

1,900

2,140

1,860

2,020

1,940

2,060

2,140

1,980

1,980

2,100

2,260

2,100

2,100

2,100

2,060

2,020 1,980

2,180

2,220

1,8201,860

2,020

1,940

Qghcy

Qgtow

Cl

Cll Khgd Crg

Qgtow

Qgtow

Qc Qsltsd

Qsltsd

Qgcu

Qcg

Qc Qc

Qc

Qc

Qc

Qcg

Qcg

Qcg

Qgcu Qgcu

Bu

Bu

Qsltsd

Qfmg

Ql

Qllb

Ql

Qllb

Qllb

U.S. Navy 

Acoustic 

Research 

Detachment 

Base

Jökulhlaup Point

G

G

I

G E

C

C

B

B

B

A

A

A

B

B

D

D

E

E

I

H

A

A

B

H I

G

A. Scenic Bay

Bayview

116°33'30"W 116°33'W 116°32'30"W 116°32'W

47°

59'N

47°

58'

50"N

47°

58'

40"N

47°

58'

30"N

Cape Horn Peak

0 0.1 0.2 0.3 0.4 0.5 MILE

0 0.1 0.2 0.3 0.4 0.5 KILOMETER

N

tac13-0838_fig05b

Qsltsd Qcg Qsltsd

Qgcu

Qsltsd

Qc Qgcu

Qc

Qfmg

Qcg

Qcg

Qfmg

Qfmg

Qcg Qgcu

Qc

Qc

Qcg

Qgtow Qgtow

E

E

D

D

E

A

A

A

D D

E

E

E

E

A

D

D

2,100

1,980

2,020

1,900

1,900

1,860

1,820

2,140

1,940

2,100

2,100

1,980

2,060

2,100

2,140

1,940

2,020

2,060

1,940

1,940

1,980

1,820

1,860

B. Idlewild Bay

Jökulhlaup Point

47° 47°57'20"N, 116°34'15”W 47°57'25"N 116°34'W 47°57'30"N 116°33'45”W 47°57'35"N 116°33'30”W 47°57'40"N 47°57'45"N 116°33'15”W 47°57'50"N 116°33'W 47°57'55"N 116°32'45”W 47°58'N 47°58'05"N 116°32'30”W

57'

15"N

47°

57'

10"N

47°

57'

05"N

47°

57'

15"N

47°

57'

10"N

47°

57'

05"N

0 0.1 0.2 0.3 0.4 0.5 MILE

0 0.1 0.2 0.3 0.4 0.5 KILOMETER

N

tac13-0838_fig05c

2,100

2,060

2,140

2,020

1,980

1,900

1,940

1,860

2,180

1,820

2,220

1,820

2,100

Khgd

Ywu

Ywu

Ycg

Ycg

Qcg

Yl

Yl

Qc

Qsltsd

Qsltsd Qgcu

Qgcu

A

I

F

F

F

A

H H

116°30'30"W 116°30'15"W 116°30'W 116°29'45"W

47°

57'

05"N

47°

57'N

47°

56'

55"N

Base from http://services.arcgisonline.com/arcgis/services unless otherwise noted.

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83) State Plane Coordinate System.

Elevation is referenced to National Geodetic Vertical Datum of 1929 (NGVD 29).

C. Echo Bay

0 0.05 0.1 0.15 0.2 0.25 MILE

0 0.05 0.1 0.15 0.2 0.25 KILOMETER

N

tac13-0838_fig06c

2,100

2,060

2,140

2,020

1,980

1,900

1,940

1, 860

2,220

1,820

1,820

2,100

2,180

116°30'30"W 116°30'15"W 116°30'W 116°29'45"W

47°

57'

05"N

47°

57'N

47°

56'

55"N

C. Echo Bay

0 0.05 0.1 0.15 0.2 0.25 MILE

0 0.05 0.1 0.15 0.2 0.25 KILOMETER

N

tac13-0838_fig01

116°32'W 115°24'W 114°16'W

48°

30'N

48°N

Sandpoint

Flathead

 Lake

LAKE PEND OREILLE

Albeni

Falls

Dam

Cabinet

Gorge

Dam

Purcell Trench

Clark Fork River

Pack River

Pend Oreille

 River

Base modified from U.S. Department of Agriculture

digital data 2011.

IDAHO

MONTANA

Cabinet Mountains

 Selkirk

Mountains

Coeur D'Alene Mountains

Lakeview

7.5 Minute

Quadrangle

Idlewild Bay

Scenic

 Bay

Echo Bay

 Bayview

 7.5 Minute

Quadrangle

Bayview

 Idaho Panhandle Region

Jökulhlaup

Point

Cape Horn Peak

Farragut

State Park

A

A'

EXPLANATION

Study area extents

Area of Map

IDAHO

MONTANA

0 5 10 15 20 MILES

0 5 10 15 20 KILOMETERS

N

tac13-0838_fig04

1,200 

1,400 

1,600 

1,800 

2,000 

2,200 

2,400 

2,600 

Feet above

NGVD 29

Idlewild Bay Scenic Bay

Qgtow Bu Bu

Bu

Normal maximum summer full pool

Jökulhlaup Point

?

? ? ?

VERTICAL EXAGERATION ×3

A A’

tac13-0838_explanation

A

Ywu

Cl

Crg

Khgd

Qgtow

Qghcy

Ql

Bu

Qc

Qgcu

Qcg

Qfmg

Qsltsd

Qllb

1,900 Elevation of landsurface and lakebed, National Geodetic Vertical Datum of 1929, interval 40 ft 

(figs. 5 and 6)

Lake stage elevation, 2,062.5 ft, normal maximum summer pool (figs. 5 and 6)

Lake stage elevation, 2,051.0 ft, normal minimum winter pool (figs. 5 and 6)

Lakebed slope represented by a gradational gray scale, in degrees, shallow slope is light

gray and a steep slope is dark grey. (fig. 6)

Direction of glacial Missoula flood outbursts (fig. 5)

Location of photograph extracted from underwater video of the lakebed: provides basic data about 

substrate embeddedness and geologic characteristics. The series of white dots follow transects 

of continuous video of lakebed (fig. 6)

Letters A–E are example areas used to describe the relation between lake morphology and lakebed

geologic characteristics including embeddedness (fig. 5)

Lakebed geology (figs. 4 and 5)

Landslide deposits, slope failure sent rock debris plunging into Lake Pend Oreille (this study).

Outwash deposits – poorly sorted, coarse boulder outwash gravel that records the melt water flow 

to the Pend Oreille River. Graded to the outlet of Pend Oreille Lake at Bayview at an elevation of 

2,200 feet above NGVD 29.

Bouldery till and outwash deposits – non-sorted, bouldery clay till and boulder outwash deposits that

form a modified end moraine at the south end of Lake Pend Oreille at Bayview, Idaho.

Hornblende-biotite granodiorite – gray, medium-grained, hornblende-biotitegranodiorite. Mafic mineral

content varies, and unit probably is composed of multiple plutons or plutonic phases (Lewis and 

others, 2002).

Rennie Shale and Gold Creek Quartzite – shale is a fissile olive-colored fossiliferous shale. 

Underlying the shale is white to pale pink, vitreous coarse-grained quartzite (Lewis and 

others, 2002).

Lakeview Limestone – light to dark gray, thin- to thick-bedded, blocky limestone (Lewis and others, 

2002). Unit was mined for lime at Bayview (Savage, 1965).

Wallace Formation, upper member, undivided – predominantly dark gray siltite and argillite, but 

locally contains unmapped carbonate intervals (Lewis and others, 2002).

Terrestrial geology (figs. 4 and 5)

Landslide deposit on lakebed, terrestrial slope failure send rock plunging into Lake Pend Oreille

Embedded lakebed – areas of the lakebed where 15–100 percent of the interstitial space between

gravel and cobbles is embedded with silt and sand. Gravel, cobble, or boulders may be exposed on 

lakebed.

Fine-medium gravel lakebed – well to poorly sorted, vf to m gravel forms more than 50 percent of 

this unit, may or may not include c-vc gravel, cobble, boulders, or traces of sand and silt.

Course-gravel lakebed – well to poorly sorted, c to vc gravel represents the largest percentage of clast 

in unit, may or may not include f-vf gravel, cobble, boulders, or traces of sand and silt.

Undifferentiated gravel and cobble lakebed – moderate to poorly sorted, undifferentiated, vf-m gravel 

sediment and c gravel-cobble sediment comprise this unit. Boulders may be present.

Cobble lakebed with some f-vc gravel – moderate to poorly sorted, cobble and c-vc gravel represents 

the largest percentage of clast in unit, and may include some vf-m gravel. Boulders may be present.

Bedrock

EXPLANATION

 Substrate embeddedness, percent (fig. 6)

0 - 4

5 - 15

16 - 35

36 - 65

66-100

[f., fine; m., medium; c., coarse; v, very; ft, foot; (1) Unit is mapped where gravels and cobbles on the 

lakebed are embedded with 0–15 percent silt.]

Other symbols

Pleistocene

Pleistocene

Holocene

Cretaceous

Precambrian, 

Belt supergroup Undifferentiated 

Cambrian

MN

GN

0° 19 ́

6 MILS 

15° 24 ́

274 MILS

2011 MAGNETIC NORTH DECLINATION 

Table 1. Sediment particle-size classification.

[Size terms: after Wentworth, 1922]

Size terms Size range

(inch)

Boulder Greater than 10.1

Cobble 2.5–10.1

Very course gravel 1.26–2.5

Course gravel 0.63–1.26

Medium gravel 0.31–0.63

Fine gravel 0.16–0.31

Very fine gravel 0.08–0.16

Sand, silt, and clay Less than 0.08

Description of the Morphology, Lakebed Facies, and Embeddedness in the 

Shore Zone, Rise Zone, and Open Water in Bays and Mainstem of Lake 

Lakebed with a gentle, moderate, steep, and very steep defined as 0–20, 20–40, 40–60, and greater than 60 degrees, respectively.

Clean substrate defined as less than 4 percent embeddedness, slightly embedded substrate defined as 4–15 percent 

embeddedness, and heavily embedded substrate defined as 15–100 percent embeddedness. 

Shore zone morphology is subdivided into the variable zone and subvariable zone. Variable zone is where lakebed elevations 

are between normal maximum summer full pool and normal minimum winter low pool; this zone has a gentle to moderate sloping 

lakebed and is steep and narrow along most bedrock shorelines. Subvariable zone is where lakebed elevations are lower than 

the lake’s normal minimum winter low pool elevation, and has a moderate to steep slope. This zone forms a transition to open 

water, rising somewhat abruptly from the open water. The variable zone is subdivided: the inner variable zone is the area near 

the shoreline, the middle variable zone is the area near the zone’s midpoint, and the outer variable zone is the area adjacent to 

the subvariable zone.

Labels A–I identify characteristics in the shore zone, rise zone, and open water in figure 5.

A Open water with a gentle-steep sloping lakebed, forms a lake-wide patch of heavily embedded substrate.

B Variable and subvariable zones located deep within a bay with large patches of heavily embedded substrate. Zone is shielded 

from heavier winds on main stem of the lake, and therefore, is subject to less wave action.

C Variable zone in bays with patches of clean, slightly embedded gravel and cobble substrate, and the adjacent subvariable 

zone is embedded. Sometimes a patch is limited to the upper variable zone where wave effect is greatest, likely to occur in 

areas of a bay where it is sheltered from winds.

D Variable and subvariable zones in bays have patches of clean, slightly embedded gravel and cobble substrate. Zone is likely 

to occur in areas of a bay that are less shielded from winds and wave action.

E Subvariable zone in bays with patches of clean, slightly embedded gravel-cobble substrate. Patches parallel the shoreline, 

length ranges from a few hundred feet to one-half mile, and water depth can be greater than 75 feet deep during normal 

maximum summer full pool. Either (1) the adjacent variable zone has a highly embedded substrate, or (2) the inner variable zone 

has narrow patches of clean, slightly embedded gravel-cobble substrate and highly embedded substrate in the middle and outer 

variable zones. Zone is more likely to occur in areas of a bay that are less shielded from winds and wave action.

F Shore zone on main stem of lake has (1) a variable zone with a contiguous patch of clean gravel-cobble substrate, and (2) a 

subvariable zone with a contiguous patch of clean-slightly embedded cobble substrate with a few patches of gravel and cobble. 

Generally, the main stem of the lake has stronger winds and greater wave action than bays; the wave action suspends and 

removes fines from clasts and transports clasts.

G Rise zone, where lake morphology forms an irregular, pod-like shaped rise that extends from the outer variable zone toward 

open water. This rise has a glacialfluvial gravel and cobble substrate of variable embeddedness and is surrounded by deep 

water. The rise is of glacial origin and not related to any post-glaciation or recent activity.

H Very narrow shore, steep sloping lakebed composed of bedrock. The shoreline often has a narrow patch of gravel-to-boulder 

size clasts, and embeddedness generally is less than 4 percent.

I Very narrow shore, steep terrain bordering the lake. Recent landslides have sent rock debris plunging into the lake. Clasts on 

lake bottom are angular and range in size from gravel to boulders.

Abstract

Kokanee salmon (Oncorhynchus nerka) are a keystone species in Lake Pend Oreille in northern Idaho, historically 

supporting a high-yield recreational fishery and serving as the primary prey for the threatened native bull trout (Salvelinus 

confluentus) and the Gerrard-strain rainbow trout (Oncorhynchus mykiss). After 1965, the kokanee population rapidly declined 

and has remained at a low level of abundance. Lake Pend Oreille is one of the deepest lakes in the United States, the largest lake 

in Idaho, and home to the U.S. Navy Acoustic Research Detachment Base. The U.S. Geological Survey and Idaho Department 

of Fish and Game are mapping the bathymetry, morphology, and the lakebed geologic units and embeddedness of potential 

kokanee salmon spawning habitat in Lake Pend Oreille. Relations between lake morphology, lakebed geologic units, and substrate 

embeddedness are characterized for the shore zone, rise zone, and open water in bays and the main stem of the lake. This detailed 

knowledge of physical habitat along the shoreline of Lake Pend Oreille is necessary to better evaluate and develop kokanee 

recovery actions.

Introduction

Fishery recovery efforts by the Idaho Department of Fish and Game at Lake Pend Oreille in northern Idaho (fig. 1) have 

included efforts to increase the population of kokanee salmon (Oncorhynchus nerka; fig. 2). Kokanee salmon are a keystone 

species in the lake, historically supporting a high-yield recreational fishery and serving as the primary prey for the threatened 

native bull trout (Salvelinus confluentus) and the Gerrard-strain rainbow trout (Oncorhynchus mykiss). Kokanee were introduced 

in the 1930s by downstream dispersal from Flathead Lake, Montana. They quickly became established and provided an important 

fishery from the 1940s to the early 1970s (Simpson and Wallace, 1982; Bowles and others, 1991). Annual kokanee harvests 

averaged more than 1 million fish from 1951 to 1965 (Simpson and Wallace, 1982; Paragamian and Bowles, 1995). After 1965, 

however, the kokanee population rapidly declined and has remained at a low level of abundance. Since 2000, the Lake Pend 

Oreille kokanee fishery has been closed to harvest. 

The primary factor believed to be responsible for the initial kokanee population decline was the altered lake level regime 

created by the construction and operation of the Albeni Falls Dam (Maiolie and Elam, 1993). The dam was constructed on the 

Pend Oreille River in 1952. Prior to dam operation, natural lake-level fluctuations allowed wave action to redistribute gravels 

and to remove fine sediment from gravels above the minimum pool elevation, which varied annually. These gravels provided 

spawning habitat for kokanee, which spawn along the lakeshore during November and December. The lake level has been 

monitored since 1929 at the U.S. Geological Survey stage gage at Hope, Idaho (12392500). The pre-dam-era maximum lake-level 

elevation was 2,071.62 feet (ft) above National Geodetic Vertical Datum of 1929 (NGVD 29) on June 9, 1948, and minimum 

lake-level elevation was 2,046.27 ft on February 17, 1936 (fig. 3). Since the construction of the Albeni Falls Dam, a maximum 

lake level of 2,062.5 ft above NGVD 1929 (figs. 4–6) has been maintained during the summer (normal maximum summer full 

pool), with drawdowns in autumn to reach a minimum winter level. Before 1966, the winter lake level was variable, and an 

exceptional fishery continued with the Albeni Falls Dam in operation. After 1966, however, consistent deeper drawdowns to an 

elevation of 2,051.0 ft above NGVD 1929 reduced the quantity and quality of spawning substrate (normal minimum winter low 

pool). Wave action continued to create suitable spawning habitat when the lake level was greater than 2,051.0 ft elevation; this 

habitat was above the waterline during kokanee spawning. The kokanee were forced to spawn in depths that were never exposed 

to wave action and that contained a high amount of fine sediment (Fredericks and others, 1995). Concurrent with the operational 

change at the Albeni Falls Dam, the kokanee population began to decline rapidly. The area between the normal maximum summer 

pool and the normal minimum winter pool is referred to as the variable zone (figs. 5 and 6). 

A lake-level experiment began in 1996 to improve spawning habitat and to increase kokanee recruitment. With few 

exceptions, the winter lake level was set either at an elevation of 2,051 ft , the normal minimum winter low pool level, or at 2,055 

ft, a higher level at which to submerge higher-quality spawning substrates. This strategy is still being evaluated, and questions 

remain regarding the specific habitat conditions required for successful spawning and the amount of suitable spawning habitat 

needed to provide sufficient recruitment to meet recovery goals. Additionally, augmenting the amount of suitable kokanee 

spawning habitat through means other than winter pool management, such as adding substrates, is being considered. 

The U.S. Geological Survey and Idaho Department of Fish and Game are cooperatively investigating the bathymetry, 

morphology, and lakebed geologic characteristics of potential kokanee salmon spawning habitat in Lake Pend Oreille because 

detailed knowledge of physical habitat along the shoreline of Lake Pend Oreille is necessary to better evaluate and develop 

kokanee recovery actions. Previous habitat evaluations were limited to shallow depths and were completed prior to recent 

technological advances in underwater mapping and videography techniques. The purpose of this study was to collect and analyze 

physical habitat data from several areas at the southern end of Lake Pend Oreille. Three study units were selected because they 

support most kokanee spawning activity and collectively represent a diversity of habitat conditions that are used by kokanee 

during spawning (fig. 1). The objectives of this study were to: (1) develop a high-resolution bathymetric map for each study unit, 

(2) develop a high-resolution lakebed slope map for each study unit that can be used to describe morphological characteristics, 

and (3) develop a map of lakebed geologic characteristics for each study unit.

Setting

Lake Pend Oreille in northern Idaho is 65 miles (mi) long, has a surface area of about 148 square miles (mi2), and reaches a 

maximum depth of more than 1,150 ft. It is one of the deepest lakes in the United States (The Columbia Electronic Encyclopedia, 

2012). The lake is fed by the Clark Fork and Pack Rivers, and it drains into the Pend Oreille River. The study area was in the 

southernmost part of the lake in three study units (fig. 1), each representing a different landscape. The largest study unit, in 

Scenic Bay, includes 254 acres and 2.8 mi of shoreline bordered by a gentle-to-moderate-sloping landscape and steep mountains. 

A second study unit, along the north shore of Idlewild Bay, includes 220 acres and 2.2 mi of shoreline bordered by a gentle-tomoderate-sloping landscape. Scenic Bay and Idlewild Bay are separated by a low-lying peninsula that juts into the lake; both bays 

are within the Bayview 7.5-minute quadrangle. The smallest study unit, in Echo Bay, includes 48 acres and 0.7 mi of shoreline 

bordered by steep mountains; the study unit is within the Bayview and Lakeview 7.5-minute quadrangles.

The local geologic history and formation of Lake Pend Oreille is summarized briefly here as background information about 

the evolving morphology and substrate geological characteristics of the lake. The most recent research suggests that the location 

of the lake is related to an older river valley controlled by faults (Breckenridge and Sprenke, 1997). The lake substrate consists 

mainly of silt, sand, gravel, cobble, bedrock debris, some boulders, and some bedrock outcrops. Unconsolidated sediments in the 

substrate originate mainly from glaciation, megaflood, lacustrine, and terrestrial and subaqueous landslide processes, and from 

tributary inflows. The Idaho Panhandle is widely known as a region of Precambrian Belt Supergroup sedimentary formations 

(Savage, 1965). The Wallace Formation, consisting mainly of siltite and argillite, borders the Echo Bay study unit. Cambrian-age 

formations, such as the Lakeview limestone that was mined at Bayview, are present along the north shore of the Scenic Bay study 

unit and, in some areas, form a small part of the lakebed (Lewis and others, 2002). Both the Precambrian- and Cambrian-age 

formations form steep slopes that frequently develop rockslides that plunge into the lake. The slide material in the lake includes 

large boulders that, over time, weather into smaller fragments. Pleistocene glaciation played a significant role in modifying the 

preexisting landscape (Week and Thorson, 1983; Smyers and Breckenridge, 2003). The eastern lobe of the Cordilleran Ice Sheet 

advanced from Canada into the Purcell Trench and dammed the Clark Fork River many times to form glacial Lake Missoula 

(Booth and others, 2003). The south end of Lake Pend Oreille at Farragut State Park marks the location of the breakout of the 

Missoula floods. Lake Pend Oreille was carved repeatedly by this lobe of Pleistocene ice, scoured by ice-age floods, and filled 

with glacial outwash and flood deposits. The lake is now dammed at the south end by thick glacial and flood deposits that underlie 

Farragut State Park. Wait (1985) interpreted carbon-14 evidence to show that Glacial Lake Missoula existed only between 17,200 

and 11,000 years ago. After the last flood, a glacier again occupied the lake, but this glacial advance did not result in catastrophic 

lake drainage. Quaternary-age glacial deposits border the lake and form large swaths of the lakebed. Outwash—deposits from 

glacial meltwater composed of layers of gravel, sand, and clay—covers the lower elevations at Bayview, is mapped as geologic 

unit Qgtow, and extends into the lake some undetermined distance. Bouldery till and outwash deposits are mapped as Qgtow on 

the small peninsula, Jökulhlaup Point, between Scenic Bay and Idlewild Bay. These deposits form an undisturbed end moraine at 

the south end of the lake and constitute an undetermined amount beneath the lake itself (Breckenridge and Sprenke, 1997).

Methods

Data collection methods included mapping of the lake bathymetry using an echo-sounder and collecting video imagery of the 

lakebed (fig. 7).

Shoreline and Lakebed Topographic Elevation and Morphology

Lake bathymetry was mapped using a multibeam echosounder (MBES). Results from the MBES then were used to plan 

stationing for the video survey. The MBES system included a flat-array transducer that sent a 240-kilohertz pulse over a 120-degree 

swath width. The MBES was set to receive 240 beams, each with a width of 0.75 degrees. In most areas, the MBES survey had 

about 50-percent swath overlap, which resulted in several soundings per square foot of lakebed. A contiguous, 3.28-ft digital 

elevation model (DEM) was generated from the MBES bathymetric data for each study unit. During 2010, the U.S. Army Corps 

of Engineers oversaw a LiDAR (light detecting and ranging) survey along the lake edge. The MBES and LiDAR DEMs generally 

overlapped because the LiDAR was flown at normal minimum winter pool and the MBES data were collected during the normal 

maximum summer full pool. These DEMs were combined to form a larger, seamless DEM; where the two datasets overlapped, the 

MBES data were selected solely for generating maps of the shoreline and lakebed topographic elevation (figs. 5 and 6). The slope 

of the shoreline and lakebed, shown in figures 5 and 6, was computed in degrees based on the topographic elevation DEM.

Video Imagery of Lakebed

During August 2011, video imagery of the lakebed was recorded continuously along 30 mi of lake transects (fig. 6). Transects 

typically were oriented about perpendicular to the shoreline, and video data were collected to a maximum depth of about 240 

ft. More than 200 video clips were recorded using an underwater color video camera suspended vertically in the water column. 

Two underwater laser pointers were mounted outside the camera housing and pointed downward to illuminate a reference scale 

of 4 inches (in.) on the lakebed (fig. 7). The camera was lowered through the water column until it was near the lakebed and the 

substrate could be identified. The signal from a mapping-grade Global Positioning System (GPS) receiver was output to a video 

titler to add date, time, and geospatial coordinates to the recordings. Video processing included de-interlacing, image filtering, 

and automatic still (photograph) extraction. About 20,000 photographs were extracted from the video and viewed briefly. Basic 

information about each photograph was entered into a spreadsheet: photograph file name, study area unit name, and date. These 

groupings of photographs were subsampled to reduce the number of photographs to a reasonable size that represents how substrate 

conditions vary within each study unit: 2,100 photographs were subsampled for Scenic Bay, 1,710 photographs were subsampled 

for Idlewild Bay, and 245 photographs were subsampled for Echo Bay. These photographs were reviewed, and additional 

information was added to the spreadsheet, including geospatial coordinates, embeddedness of lakebed, particle size classification, 

woody debris, macrophytes, and general comments. 

Lakebed Geologic Characteristics 

Kokanee spawning substrate preferences were considered during the development of geologic units and maps of substrate 

geologic characteristics. The two primary characteristics considered important to successful spawning and egg incubation were 

embeddedness and riverbed geology. Embeddedness is the degree to which fine sediments such as sand, silt, and clay fill the 

interstitial spaces between rocks on a substrate. A 0-percent embeddedness means that there are no fine sediments on a substrate. 

A 100-percent embeddedness means rocks are completely surrounded and covered by sediment. The sediments and rock on the 

lakebed are mapped as geologic units. The designation of lakebed geologic units that are composed of unconsolidated sediments 

is based on particle size using the Wentworth scale (Wentworth, 1922; table 1).The habitat conditions kokanee prefer for spawning 

in Lake Pend Oreille are not fully understood, but the Idaho Department of Fish and Game was investigating kokanee spawning 

habitat preference during 2012. However, it is generally accepted that kokanee spawn over clean gravel, and kokanee likely will 

spawn over smaller-diameter gravel than will larger species of salmonids. For the purposes of this study, fine substrates (silt and 

sand) were combined in a single category because neither silt nor sand is considered a preferred kokanee spawning substrate. 

Based on these general spawning substrate preferences, areas of lakebed with embeddedness of greater than 15 percent were 

classified as the geologic unit Qsltsd, “embedded lakebed.” Substrate characteristics assumed to be most preferred by spawning 

kokanee may be found in the geologic unit Qfmg, “fine-medium gravel lakebed,” where very-fine-to-medium gravel composes 

more than 50 percent of the lakebed with or without lesser amounts of coarse gravel and cobble. Kokanee also may find suitable 

spawning substrate in the geologic unit Qcg, “coarse-gravel lakebed,” where coarse and very coarse gravel compose the largest 

percentage of clasts in this unit. Substrate characteristics that spawning kokanee may avoid are in the geologic unit Qc, “cobble 

lakebed,” where cobble and coarse gravel compose the largest percentage of the clast size. Lakebed with significant amounts of 

both fine-medium gravel and coarse gravel and cobble are mapped as the undifferentiated, geologic unit Qgcu.

The terrestrial geologic units on the geology maps are from previously published maps (Lewis and others, 2002) as well 

as those developed specifically for this project; they are considered informal, local geologic units. ESRI ArcGISTM was used to 

create lakebed embeddedness maps and lakebed geologic characteristics maps based on the analysis of photographs extracted 

from the video recordings (figs. 5–7). Lakebed bathymetry and slope are shown on these maps to help clarify the relation between 

Figure 5. Shoreline and lakebed topographic elevation and terrestrial and lakebed geology at (A) Scenic Bay, (B) Idlewild Bay, and (C) Echo Bay, Lake Pend Oreille, Bayview and Lakeview 

quadrangles, Idaho. Figure 6. Shoreline and lakebed topographic elevation, bed slope, and embeddedness of lakebed sediments at (A) Scenic Bay, (B) Idlewild Bay, and (C) Echo Bay, Lake Pend Oreille, Bayview and 

Lakeview quadrangles, Idaho.

Figure 1. Study area and surrounding rivers, lakes, and dams at Lake Pend Oreille, Idaho. See figure 4 for geologic cross section A–A’.

Figure 3. Mean daily water-surface elevation at Lake Pend Oreille at Hope, Idaho, U.S. Geological Survey 

stage gage 12392500, water years 1930–2012. 

Figure 2. Kokanee salmon (Oncorhynchus nerka), a keystone species in Lake Pend Oreille, Idaho.

Figure 4. Generalized geologic cross section A–A’ of Lake Pend Oreille study area and 

surrounding areas near Bayview Idaho. See figure 1 for cross section location.

Figure 7. Underwater photographs showing types of bedrock and glaciofluvial geology that form the bed of Lake Pend Oreille, Bayview and Lakeview quadrangles, Idaho, 2011. 

Laser scale is 4 inches.

lake morphology, lakebed geologic units, and substrate embeddedness. Descriptions of the morphology, lakebed geology, and 

embeddedness in the shore zone, rise zone, and open water in bays and the main stem of the lake are provided in figures 5–6. 

Lakebed geologic units and embeddedness are subject to change in shallow parts of the lake, especially the shore zone, where 

wave action can suspend and remove fines from clasts and transport them to other areas, and can also transport and sort clasts.

Acknowledgments 

The authors wish to thank the U.S. Navy Acoustic Research Detachment at Bayiew, Idaho, for providing logistical support 

for this project in the form of a covered slip with power to house the U.S. Geological Survey research vessel. Additionally, we 

thank the residents along the shore of Lake Pend Oreille, who have been very accommodating to the U.S. Geological Survey 

research vessel collecting data near their shoreline and boat docks. Theresa Olsen, U.S. Geological Survey, Washington Water 

Science Center, provided technical guidance for ArcMap applications used to develop the lakebed morphology and geology 

maps presented in this report.

References Cited

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Bathymetry, Morphology, and Lakebed Geologic Characteristics of Potential Kokanee Salmon 

Spawning Habitat in Lake Pend Oreille, Bayview and Lakeview Quadrangles, Idaho

By

Gary J. Barton, U.S. Geological Survey, and Andrew M. Dux, Idaho Department of Fish and Game

2013

Prepared in cooperation with the

IDAHO DEPARTMENT OF FISH AND GAME

U.S. Department of the Interior

U.S. Geological Survey

Base maps from http://services.arcgisonline.com/arcgis/services unless otherwise noted.

Horizontal coordinant information is referenced to the North American Datum of 1983 (NAD 83) State Plane Coordinate System.

Elevation is referenced to National Geodetic Vertical Datum of 1929 (NGVD 29).

SCIENTIFIC INVESTIGATIONS MAP 3272

Bathymetry, Morphology, and Lakebed Geologic Characteristics 

Barton, G.J., and Dux, A.M., 2013, Bathymetry, Morphology, and Lakebed Geologic Characteristics of Potential 

Kokanee Salmon Spawning Habitat in Lake Pend Oreille, Bayview and Lakeview Quadrangles, Idaho

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