Michigan Department of Natural Resources
Cass County (T5S, R13W, Sections 23, 24, 26, 27, 28, 29, 30)
Surveyed June 1996
James L. Dexter, Jr.
The Rocky River is a marginal trout stream with most of the potential trout water located in the northeastern corner of Cass County. The stream exits Cass County as a third-order stream, and continues into St. Joseph County where it enters the St. Joseph River in the town of Three Rivers. The headwaters are classified as top-quality coldwater, while the remainder of the stream (starting just south of Marcellus) is classified as second-quality coldwater.
Flowing through a patchwork of active and fallow farmland, swamps, and small blocks of forests, the Rocky River exhibits moderate summer flows (roughly 50-75 cfs). Flood flows can become very high, especially near Three Rivers, where flows in excess of 900 cfs have been recorded. The majority of the watershed lies in well-drained loamy soils that encompass nearly level land to moderately rolling hills. The watershed is large, encompassing more than 100,000 acres upstream from Floating Bridge Road (P. Seelbach, Institute for Fisheries Research, personal communication).
There are 13 tributaries to this stream system. Since 1967, three tributaries
have been classified as top-quality coldwater, two as second-quality coldwater,
seven as top-quality warmwater, and one as second-quality warmwater. About
half of the tributaries start as springs, the other half originate as
outlets of small lakes. Flowerfield Creek is the largest tributary, entering
the Rocky River in the middle stretches of St. Joseph County. This coldwater
tributary virtually doubles the size of the river.
The Rocky River is estimated to be 25 miles long. Stream width averages 32 feet and depth averages 1.5 feet. Habitat varies considerably from section to section. Undercut banks, logs, aquatic vegetation, and overhanging brush are common to all areas. Channel sinuosity, the number of pools, and in-stream brush vary from abundant to lacking. In the headwaters, bottom substrates are mostly silt, sand, and gravel, with some clay. Substrates in the middle portions are composed of 50% sand, equal amounts of gravel and silt, and a trace of rock rubble. The lower sections are mostly rock rubble, gravel, and sand, with some silt. The Rocky River falls approximately 90 feet from its source to its confluence. Water quality characteristics collected during a 1990 survey included alkalinity (144-214 ppm), pH (7.5), and dissolved oxygen (7.9-9.1 ppm). No historical data could be found concerning those characteristics.
Development along the river is limited to farms. One remnant dam exists on the mainstream, at the confluence with the St. Joseph River. In December 1992 this low head, rock-rubble structure failed and washed out. The structure had not been fixed as of February 2000. The City of Three Rivers is now considering an off-channel pond to substitute for the old dam. No state ownership exists along the banks. Access is available with permission of landowners.
Portions of the Rocky River have been managed for trout since at least
1938. For 7 years, between 1938 and 1946, combinations of brook, brown,
rainbow trout were stocked in the St. Joseph County portions of the river.
Stocking was discontinued for 30 years, then that area received up to
10,000 brown trout yearlings in 1977, 1978, and 1986-1990. The Cass County
portion of the Rocky River was stocked with brown trout from 1977 until
recent years at the rate of 200 trout per acre.
In 1990, a fish survey covering representative stations along the entire length of the system thoroughly delineated which waters are suitable for trout and which were not (Dexter 1992). Combinations of gear (backpack shocker at upper station, 250-V DC stream shocker with 2 or 3 probes at all other stations) were used to sample fish. Based on that survey, only the headwaters appeared to be suitable for trout because brown trout (including some wild trout), mottled sculpins, white suckers, and creek chubs predominated there. The lower waters did not contain these coldwater indicator species. This led to the decision to discontinue all trout stockings in the St. Joseph County portion of the river.
For the 1996 evaluation, only two stocked sites in the better waters
of Cass County were surveyed. These sites were at M-40 and Pioneer Road.
A 250-V DC stream shocker with two probes was used to sample fish.
The fish community found in 1996 was, most likely, no different from
that of 50 years ago, and was similar to that found in the 1990 survey
(Dexter 1992). A total of 17 species of fish were identified (Table 1).
Only three brown trout were collected. One was from M-40 and two were
from Pioneer Road. One of the brown trout at Pioneer Road appeared to
be a wild fish based on its fin characteristics and color. All three trout
were age-1. Catch per hour of brown trout at Cass County stations have
declined substantially since the 1990 survey, from 22/hour to 4/hour in
1996. Minnows and miscellaneous species now predominate. Bluegill, white
suckers, and rock bass were the only other game fish collected. White
suckers were the most common and ranged from 3 to 12 inches. Bluegill
and rock bass did not exceed 7 inches in length.
After this survey was completed we contacted local conservation officers
to gain their perspective of the trout fishery. None of them had ever
encountered a trout angler in the Cass County portion of the Rocky River.
Based on this information and the poor results of the survey, it was decided
to discontinue all trout stockings into the Rocky River effective in 1997.
At the same time we made plans to collect temperature data to further
define the potential of this system for future management, and to further
support our decision to stop stocking of trout.
Wehrly et al. (1999) developed thermal classifications for Lower Michigan
rivers that can be used to describe the thermal distribution of stream
fishes and generate expectations of species assemblages. In 1999, temperature
data was gathered at Bent Road (St. Joseph County) and M-40 (Cass County).
Water temperatures were recorded every 2 hours using Ryan Tempmentors.
This information revealed that the lower Rocky River is one of the warmest
streams in the state, with a recorded maximum temperature of 93oF. The
upper portions of the Rocky River in Cass County also proved to be too
warm, exhibiting thermal characteristics very similar to the Grand River.
It appears from our records (Johnson 1972) that previous managers had
used late summer data to determine the thermal characteristics of the
stream. Hinz and Wiley (1997) found that July is the time when streams
in Michigan approach the lethal upper thermal limit for some taxa and
also when differences in temperature among sites are most pronounced.
With the information that has been gathered, it is apparent that the
Rocky River should be dropped from the designated trout stream list (F.O.
200.00). The two surveys in the 1990s indicated that upper tributaries
were capable of producing a few wild trout, but that the majority of the
system is much too warm to support a year-round coldwater fish assemblage.
It is unfortunate that the temperature data that is available to managers
today was not available when this stocking program was reinstituted in
the 1970s. Thousands of dollars could have been saved by not stocking
trout in unsuitable waters such as this.
Report completed May 15, 2000.
Dexter, J. L. Jr. 1992. Rocky River. Michigan Department of Natural Resources, Status of the Fishery Resource Report 92-4, Ann Arbor.
Hinz, L. C. Jr., and M. J. Wiley. 1997. Growth and production of juvenile
trout in Michigan Streams: influence of temperature. Michigan Department
of Natural Resources, Fisheries Research Report 2041, Ann Arbor.
Johnson, D. C. 1972. Preliminary habitat improvement report for the lower
portion of the Rocky River, St. Joseph County. Michigan Department of
Natural Resources, Inland Streams Files, Plainwell.
Wehrly, K. E., M. J. Wiley, and P. W. Seelbach. 1999. A thermal habitat classification for Lower Michigan rivers. Michigan Department of Natural Resources, Fisheries Division Research Report 2038, Ann Arbor.
Table 1.-Species, relative abundance, and length of fish collected by electrofishing at M-40 and Pioneer Road (Cass County) stations on the Rocky River, June 1996.
Last Update: 08/07/2002
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