How To Fish Stillwaters

November 22nd, 2004

Stillwaters, lakes, ponds and reservoirs are the most underutilized fisheries in the North America. Why? Because the average fly fisher doesn't know how to fish them, or where to start. Stay tuned, you too can master stillwaters! ~ LadyFisher


Limnology

By Paul C. Marriner

According to Webster, limnology is the science of the biological and other phenomena of fresh water, especially of ponds and lakes. Assuming a healthy population of fish, much of this body of knowledge has no direct application to fly-fishing success. However some has, and besides we need to establish a glossary of terms used elsewhere. One general comment concerns the word lake itself: in Scotland it's a loch, in Wales a lynn, and in Ireland a lough. I use these names where appropriate.

WHAT IS A STILL WATER?

In general, stillwaters include lakes and ponds. A stillwater is called a lake when it's large enough to have waves that create a wave-swept zone, otherwise it's a pond. Newfoundlanders, going their own way as they often do, call many of their island lakes ponds.

LAKE CLASSIFICATION

One lake classification with which many readers will be familiar is trophic status. Lakes are oligotrophic, mesotrophic, or eutrophic, depending on nutrient level. However, when considering very large lakes, like the Great Lakes, various regions of such lakes may fall into different classifications. Water clarity is an indication of trophic status.

Oligotrophic

Oligotrophic lakes have low nutrient levels, are often cold and deep, and feature close to 100% oxygen saturation. The characteristic clear water results from the lack of nutrients. Many northern glacial lakes are oligotrophic, including some which are also quite shallow. Cold temperatures and high oxygen content mean that they often support salmonid populations. Exceptions include those killed by acid precipitation. Trout do not flourish in stillwaters with a pH below 5.0.

Eutrophic

Eutrophic lakes have high nutrient levels, are usually shallow and warm, and generally suffer from low oxygen content particularly in the deepest parts. High nutrient levels create cloudy water. For example, many man-made ponds at low altitudes fit into this category and will normally support only species like carp that tolerate low oxygen levels.

Mesotrophic

It's likely that most of the world's lakes are mesotrophic, meaning that they are moderately enriched and not very deep, and can support a variety offish species.

While these are the generally accepted definitions and characteristics, trout anglers will know that they don't always apply. Some of our best trout fisheries are eutrophic lakes with cold water sources or ones that are located at a high enough altitude to stay cool. Within this group are stillwaters that need oxygen supplied artificially. Of these, some need oxygen to prevent winterkill, while others need it in summer as well. Many of these eutrophic lakes are so rich that they suffer mightily from algae blooms during the hottest months.

GEOLOGICAL CLASSIFICATION

Another way to deal with lakes relates to their origin, with one text in my library listing twenty-eight types; interesting stuff but of little practical use. One exception is when knowing how a stillwater was formed leads to searching out specific fish-holding structure like an old river bed in an impoundment. One estimate suggests that more than two-thirds of all lakes in the northern latitudes are glacial in origin, but as the local geography usually determines their trophic status such a description is of little help. Some types of stillwaters referred to later may be unfamiliar and so their descriptions follow.

(Precambrian) Shield Lakes

The Precambrian Shield is a vast horseshoe-shaped area around Hudson Bay covering eastern and central Canada, and a small part of the northern United States. The rocks contain large areas of granite and the lakes gouged out of the shield by glaciation are numerous, often long and narrow, and oriented in the direction of the glacier's retreat. Many of these lakes are oligotrophic and support salmonids. Kettle lakes are another glacial remnant. They were formed when large blocks of glacial ice melted into relatively shallow spring-fed depressions. Because the surrounding glacial debris (moraine) is often rich in pH boosting minerals, these lakes support abundant fish populations. They are found scattered throughout the shield, including easily accessible areas in central Canada and across the northern tier of adjacent US states. In other parts of the world these lakes are sometimes called tarns. Tens of thousands of kettle lakes are found in the far north but they are of little interest to fly-fishers.

Bogan

A bogan is a stillwater formed by a cold-water stream in the interval (or flood plain) of a large river or an inlet stream removed from the general shoreline of a lake. The size is variable depending on the distance between the stream mouth and the main river or lake, but all those I have encountered would be considered ponds. When associated with rivers, water from the bogan usually enters the main river over a shallow bar. In summer, bogans are generally colder than the main river or lake, and often offer shelter to trout.

Although not called bogans, a similar coastal phenomenon produces small freshwater ponds, often behind beaches. Like bogans the inlets and outlets are generally small, however if the pond is large enough it may support a resident trout population (some are stocked) or be visited by anadromous species.

Pothole Lakes

Author Paul
One area where anglers cross swords with scientists is in the definition of pothole lake. The limnologists consider these to be lakes created by fluvial (i.e., river) forces. However, when most of us speak of pothole lakes, we mean small ponds, usually on the prairies, created naturally (much like kettle lakes but rarely as deep) or artificially in local depressions and supplied by springs. What the scientists refer to as a pothole I generally call a river stillwater.

Tarn

Tarn is defined in the dictionary as a high mountain lake. However, at least in my experience, the word is also often used to describe a medium-sized, shallow, high-plateau lake, usually mesotrophic. In most ways they resemble a prairie pothole, just larger and higher in elevation. ~ PCM

More next time on Limnology.

Credits: Excerpt from Stillwater Fly Fishing, Tools & Tactics By Paul C. Marriner, published by Gale's End Press. We appreciate use permission.

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