After the Second World War, Lemmenjoki was hit by two major upheavals. In 1945, Niilo, Uula and Veikko Ranttila found gold in Morgamoja, which started a gold rush in Lemmenjoki. At its peak in the 1950s, almost one hundred claims were active. The gold rush in Lemmenjoki started to die down towards the end of the decade, however, and things went quiet for several decades.

New interest in gold mining awakened in the 1970s with the launch of World Gold Panning Championships in Tankavaara and the new gold museum. This turned out to be a significant decade in Lemmenjoki, during which the old and new generations of goldminers met. The old generation disappeared to the happy prospecting ground in the 1980s, while the new one applied the lessons learned from their seniors to a new mechanical method. It made processing multiple layers of soil possible and the more professional activities could now earn you a living, but it also set goldminers on a collision course with nature conservation.

Lemmenjoki National Park was established in 1956, however followed by almost ten years of planning. While the first national parks and nature reserves in Finland were established in 1938, most of them were lost in the war. This is why the leading natural science associations in the country submitted a proposal to the Government on the establishment of new nature reserves in 1949.

With this in mind, the Government appointed a committee that produced its proposal in 1953. The proposal included the establishment a national park of a 511 km2 in Lemmenjoki. The justification for the proposal was the pristine forests of great natural beauty in the river valley. The committee also wanted to include the fells surrounding the forest in the park to ensure that it was a sufficiently large ecological entity. The national park established in 1956 ultimately was no more than 385 square kilometres in surface area. Such areas as the best-known goldmining sites were left outside the park’s boundaries.

Even after the parks established in 1956, it was felt that the Finnish national park network was not particularly representative. This is why a plan for new protected areas on state-owned lands in northern Finland was drawn up as soon as 1968. As part of this plan, Lemmenjoki National Park was extended in 1971. The plans for Övre Anárjohka National Park in Norway were a key reason for this expansion. Lemmenjoki National Park was consequently expanded all the way to the Norwegian border, resulting in a large, unified protected area. This meant that the goldmining sites were also included in the National Park.

The National Park reached its current size in 1981. Following a proposal of the National Parks Committee made in 1977, areas in Paadarskaidi on the south side of the road linking Tirro and Angeli and extensive mires in the border areas of Inari and Kittilä were attached to it. This expansion caused more controversy than the previous one, as the protection of Paadarskaidi pine forests, in particular, was considered a threat to forestry jobs. The Committee's original proposal was consequently scaled back regarding Paadarskaidi.

A conflict between goldminers and the National Park arose in the late 1980s and early 1990s, as the pace of mechanical excavation accelerated and caused turbidity in waters downstream from the claims. A resolution to the dispute between Metsähallitus and the goldminers was sought in many court proceedings, as the relevant acts and decrees were partly unclear. While mechanical excavation was finally banned in 1991, it was allowed to go on in existing claims, which were converted into mining districts. An update of the Mining Act in 2011 stopped mechanical goldmining also in these districts after a transition period in 2020. Manual goldmining still goes on in Lemmenjoki.

The Sauna in the Vaskojoki Opern Wilderness Hut in Lemmenjoki National Park is not in use