The mission of the Green Lake National Fish Hatchery is to propagate Atlantic salmon for restoration and recovery rivers in the Gulf of Maine

History of the Green Lake National Fish Hatchery

The Green Lake National Fish Hatchery is currently one of the 28 fish hatcheries and fishery management offices in the Northeast Region of the United States Fish and Wildlife Service (Region 5).  The Maine Fisheries Complex, located at the Craig Brook National Fish Hatchery in E. Orland, Maine, is comprised of the Craig Brook National Fish Hatchery, the Green Lake National Fish Hatchery (located in Ellsworth, Maine) and the Maine Fishery Resource Office (located at Craig Brook NFH).  Green Lake Hatchery rears approximately 1,000,000 fish annually. The primary life stages produced at this facility are Atlantic salmon smolts and parr. These annual releases currently account for 70% of the USA home water returns of adult Atlantic salmon.

Green Lake NFH was built in three phases with original construction in 1973, a second phase of construction in 1976, and the water treatment building was completed in 1978. Pictured above left is the Hatchery circa 1977. In the foreground, the twenty-foot tanks are being buried.  Later, a structure was built over the tanks and fencing and shade panels were added.  These tanks now house parr through the winter months as they develop into smolts and until they are ready for distribution to Gulf of Maine rivers in the spring.

At left, the outdoor tanks are shown finished and in operation under the huge structure affectionately dubbed “The Big Top” by Hatchery staff.  The Big Top is a large covered rearing area approximately 300` x 130` equipped with thirty-four 20-foot tanks as well as sixty-eight 30-foot tanks.  This area can house up to one million fish at one time.  The gray boxes attached to the tanks represent the automatic feeding system.

Layout of the "Big Top" at Green Lake NFH

Green Lake supplies the water, using a gravity feed system. We are fortunate that due to the topography of the hatchery site, no pumping of water is required to operate the hatchery.  Water is treated with filters and ultraviolet radiation at the hatchery’s water treatment plant to prevent fish diseases from infecting hatchery populations.

The hatchery has a plentiful source of clean water from nearby Green Lake. The water use at the hatchery varies seasonally with an average daily use of 10 million gallons. The photo to the left shows the outer cover and the micro sieve filter of a treatment unit at the plant. These filters can process 6.5 million gallons of water each day.  The filters remove suspended particles down to 20 microns in size (about the size of pollen). From these filters the water then passes on to the ultraviolet units.

The photo to the right shows the ultraviolet light system at the Hatchery’s water treatment plant.  The water passes through the filters before UV treatment. Ultraviolet light, at 254 nm wavelength, kills the bacteria and unseen microbes that potentially carry disease harmful to salmon at any stage. At the treatment plant there are five ultraviolet units.

Water Treatment Process Flow Diagram

 Each winter, eggs, received from Craig Brook National Fish Hatchery’s brood stock facility, are disinfected and placed in trays in the Incubation Room at the Green Lake National Fish Hatchery.  The trays are continuously flushed with water and maintained at a constant temperature until early February when the water is gradually heated. The water in the incubation area and nursery area is heated from 34ºF to 50ºF for about three months to advance development.  As the eggs begin to hatch (March), they’re moved to tanks in the fry nursery area.  The hatched eggs are now “fry” and remain in the nursery until they are about three months old. Fry are routinely moved from the nursery area to larger outdoor tanks to prevent over-crowding.  

The tanks in the fry nursery are heated; this effectively accelerates the growth of the salmon and shortens the time they must remain at the Hatchery.  It takes approximately 17 months to rear a smolt at the hatchery compared to 24 months in the wild (unheated water). This shortened growth window allows more smolts to be reared at the hatchery at a reduced cost when compared to rearing fish with unheated water. 

All the salmon fry are moved from the nursery area to the outside rearing area by the end of May. Here, under the “Big Top”, (photo below) they will quickly grow to 3½” parr. In early July the number of fish in each pool will have to be reduced. The fish are split into several empty pools to prevent over-crowding. During the month of September the parr, now 5½”, have again outgrown their space. 

One million fish are “crowded” into small sections of the circular tanks and the smaller parr are forced through openings in the screens, leaving the larger parr in between the screen sections. These larger fish (approximately 650,000) are moved to empty tanks where they will complete their growth cycle to become 7-8” smolts by the next spring. By the completion of grading all 102 tanks on station will be in use (station pool photo below).   The smaller parr  (approximately 350,000) will be stocked out to their natal rivers in September and October to continue their development in the wild.

When the pre-smolts reach approximately seven-inches long, (February) some of the hatchery fish are tagged.  As salmon return to Maine’s rivers at maturity, the color-coded tag enables staff to identify the fish that have been released from the hatchery as smolts in the spring. These marked fish are captured at various salmon weirs at the heads of Maine’s rivers.  The color not only indicates the river where they are released, but also what parents the fish are spawned from.

At left, the tagging process begins.  Sedated fish are injected behind the eye with a tiny colored mark to indicate river or release site origin.  When the fish are released as smolts (April-May), they will travel to Greenland via Maine rivers. Maine salmon will spend 1-3 years in the Ocean. Most Atlantic salmon return after 2 years at sea.

The colored marks are still visible on adult salmon even after two years in the marine environment.  These marked adult returns allow biologists to estimate the survival of fish and identify hatchery fish from wild adult salmon. 

In April and May, hatchery staff hand-load specially equipped distribution trucks with 8-inch smolts for release into the several rivers in the Gulf of Maine.  Approximately 650,000 smolts are released during the six-week distribution season. 

Each truck is specially equipped with an oxygenation system to maintain the proper levels of oxygen in the water while the salmon are transported.  Oxygen and water levels are constantly monitored and the salmon are released quickly.  Stocking destinations can require fish to be transported for over six hours.

The Green Lake National Fish Hatchery welcomes visitors during the hours of 8AM through 4PM for a self-guided tour.  Staff will generally be available to answer questions and educate visitors of all ages on the development of the Atlantic salmon and the mission of the United States Fish and Wildlife Service in protecting the endangered Atlantic salmon.  The hatchery offers an outreach room with videos and a living stream as well as the opportunity to experience a working Hatchery.

It should be noted that Green Lake NFH is staffed 365 days a year and hatchery operations require fish to be on station during the entire year. During the months of January and February, Green Lake National Fish Hatchery staff will be busy beginning the cycle once again.   Salmon eggs received from brood stock spawned at the Craig Brook National Fish Hatchery, will be placed in the incubation room and raised to smolts for distribution... 

This page was last updated January 23, 2004