TABLE OF CONTENTS Pages Symposium 1 - the National Sea ...

The Hatchery
The hatchery supports the Great Lakes salmon program and currently produces 78,000 kg
annually and uses up to 80,000 kg of food. The original production targets were for three
million coho salmon, but were changed to two million to reduce effluent phosphorus load. The
coho salmon are grown to 36/kg (28g/fish). In addition to the coho salmon, the hatchery
produces five million chinook salmon at 220/kg (4.5g/fish). The site also houses a coho egg
take facility.
The chinook salmon are reared indoors in large concrete raceways while final rearing of the coho
salmon occurs outdoors in Burrows rearing ponds, modified from circulation to plug-flow
design, equipped with baffles to make the ponds self-cleaning. This has significantly improved
the management of solids, contributing to further reductions in discharge of phosphorous.
The hatchery operates on three water sources. Brundage Spring delivers water to the indoor
rearing tanks at a rate of approximately 4500 lpm (1200 gpm), Brundage Creek provides about
18,000 lpm (5000 gpm) used indoors and out and Platte River allows up to 32,000 lpm (8500
gpm) of water to the outdoor raceways. This water is pumped to an elevated water distribution
reservoir to provide the required hydrostatic pressure for deliverance through underground
piping. The high quality, stable temperature, spring water can be reused by pumping it up into
the distribution reservoir to modify extreme summer river water temperatures.
The hatchery discharges into the Platte River after passing through a two hectare (5 acre)
treatment pond.
The River
The Platte River is a very stable river system, receiving abundant groundwater from the
underlying glacial geology. Its 500 km 2 watershed is approximately 90% underdeveloped. The
river has a moderate natural productivity with phosphorous concentrations typically ranging
from 20 )g/L in winter/spring down to 10 )g/L in late summer/fall. Variations may fluctuate
from 12 to 50 )g/L in May - July to less than 12 )g/L in December (Walker 1998).
The Lake
Big Platte Lake is a 10.6 km 2 (2650 acre) natural, hard water lake with a mean depth of 7.7 m
(25') and a maximum depth of 29 m (95').
Based on mean ranges for total phosphorus, total nitrogen and chlorophyll a, its classification is
oligotrophic. However, a mean Secchi depth of 2.32 m (7.6') places it in the eutrophic category
(Table 1). The reduced Secchi depth is associated directly with the development of calcium
carbonate (marl) precipitates in the lake (King 1999).
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