Born of an anger over growing threats to our nation's natural resources during the industrial boom following World War I, the IWLA is a national environmental organization with its roots in the Midwest. In Chicago in January 1922 avid angler, writer and publicist Will Dilg called together a group of fishermen to propose the establishment of a national conservation organization that would fight the "commercial exploiters of America". The gathered sportsmen wholeheartedly concurred and the organization was born, appropriately named for the 17th century fisherman and philosopher, Izaak Walton, whose The Compleat Angler espoused conservation ideals in line with those of the new organization.

Chapters were formed throughout the Midwest to rally the League's pledge "to defend soils, woods, water, and wildlife". As early as 1923 the newly formed League blocked a plan to build roads into the area that is now the Boundary Waters Canoe Area of the Superior National Forest. The IWLA was first, and for many years the only, citizens' organization involved in the preservation of the BWCAW. It has continued its commitment to that goal through its lawsuit blocking copper mining in that area and its support of federal wilderness legislation.

The League's first major accomplishment, and one in which the Minnesota Division played a big role, was the establishment of the Upper Mississippi Wildlife and Fish Refuge a vital issue since the League's inception, resulted in the first federal water pollution law. In the 1970s the League was influential in the adoption of the Clean Water Act which it continues to monitor closely.

Today the IWLA is a grass roots organization with local chapters, grouped into divisions within states, which support a national lobbying and administrative staff in Washington, DC.

A regional office is located in Saint Paul, Minnesota which concentrates on issues in the Mississippi River states with emphasis on energy efficiency, hydro-power, sustainable agriculture and the Mississippi River.

The IWLA's Minnesota Division and local chapters throughout the state are active in conservation issues through education, lobbying, and a multitude of local conservation projects.

The League has traditionally worked through the consistent and persistent support of its position with facts, reason, and consideration of the long-range public interest, and has resorted to litigation or other direction action only as a last resort in extreme situations.

In this era of single-issue specialized environmental groups, the IWLA remains a general conservation organization which over the years has earned a reputation for hard work and solid environmental positions.