Anglers fishing on Michigan's lakes and streams may be familiar with the sight of state tank trucks pulling up to the bank and releasing their contents into the water. Such occurrences are common right now as the Department of Natural Resources is in the midst of spring fish-stocking season.

Over the course of the year, the DNR will stock roughly 11 million fish into state waterways and the Great Lakes, the vast majority of them during the spring.

It's a big job. The DNR maintains a fleet of 18 trucks to stock fish across the state. Trucks range from a semi that pulls a 4,000-gallon tank to a pickup with a 300-gallon tank mounted on it. Most are double-and triple-axle tankers.

Last year, DNR fisheries personnel drove 134,000 miles to 619 sites to stock 745,000 pounds of fish at a cost of 96 cents a pound -- and that's just for transportation. (The overall hatchery program budget is $8 million annually.) Fisheries stocking personnel averaged 8.1 trips per day during the spring stocking season, each an average of 6.7 hours. In all, staff spent 3,280 hours just driving fish across the state for stocking.

Fish stocking begins in mid- to late March, explains Steve VanDerLaan, the biologist who coordinates stocking efforts for the Fisheries Division's hatchery operations. That means DNR personnel often are chopping holes in the ice to get fish into the water.

"It gets to a point that as the fish grow, we start running out of physical room in the hatcheries to carry these fish," said VanDerLaan, who works out of the Wolf Lake State Fish Hatchery. "We've got to get them out."

The bulk of stocking activity will be completed by the end of May, but there are some fish -- muskellunge, for instance, and some brown trout, that are stocked in the fall.

The bulk of the fish are cold-water species (trout and salmon) that are stocked into the Great Lakes and rivers connecting into the Great Lakes. Fisheries Division produces more than four million salmon -- mostly chinooks, but about 630,000 coho as well -- for the Great Lakes program. But other cold-water fish, such as brook trout, brown trout and rainbows, are stocked into inland lakes and streams, too.

Moving that many fish that many miles poses logistical headaches for the Fisheries Division. With six hatcheries producing fish that will be distributed almost statewide, it takes significant coordination to keep the railroad running properly.

And a fish isn't just a fish. Fact is, even a brown trout is not just a brown trout.

"Certain hatcheries raise certain strains," said Christian LeSage, a fisheries biologist in Lansing who allocates hatchery production to the various districts. "For instance, we have four strains of brown trout; some are for streams, others are intended for the Great Lakes."

The same is true for rainbow trout. Some are grown specifically for inland lakes and streams. Others are steelhead to be stocked in rivers where they'll smolt out to the Great Lakes and, it's hoped, return as adults in three or four years.

That means that sometimes fish must be trucked past hatcheries that are closer to the stocking site than where the fish were raised.

"We have to match the production with the requests, but we try to keep the distances of our trips as short as possible," LeSage said. "It's something that we have to tweak often. Every year is different. Some years we have production shortfalls among the strains so we have to allocate what we produce among all our management units' requests, and then we have to see if we can get some other strain that will work. It gets very complex."

Besides the cold-water species, the DNR raises and stocks a number of coolwater species, too, most notably sturgeon, walleyes and muskellunge. Some of them, such as sturgeon for the Black Lake system, are raised at streamside hatcheries that make transportation much less problematic. On occasion, the DNR also moves adult fish around to establish new fisheries, such as redear sunfish, but that has become more difficult in recent years because of disease concerns.

Not all the fish stocked into Michigan waterways are raised in DNR hatcheries. Channel catfish, which generally are stocked in the fall, are obtained from other states, such as Indiana and Ohio, to create inland fisheries in lakes and streams. And all of our Atlantic salmon are produced at Lake Superior State University and though most are released on-site, the DNR transports fall fingerlings to Torch Lake.

Walleyes, which are spawned in state hatcheries, are transferred to nursery ponds -- often with the assistance of non-government conservation groups -- where they can grow larger and produce better returns than if they were stocked as fingerlings. This year, the DNR hopes to stock 1.7 million walleyes, which is a reduction from the recent past because of concerns about viral hemorrhagic septicemia, an exotic fish disease that has been found in some Great Lakes waters and one inland lake. The DNR has put strict regimens into effect to prevent spreading this so-far incurable and deadly fish disease.

The DNR hopes to ramp up walleye production, as well as resume northern pike production, as soon as an effective treatment to disinfect the eggs of those species is developed. In the meantime, the Fisheries Division, which has an effective treatment for disinfecting trout and salmon eggs, will continue to produce millions of them for our lakes, streams -- and anglers.