HELENA -- The 1980s lapel buttons had been stored for years in Tom Bugni's home, leftovers from the successful campaign for a Montana law guaranteeing public access to streams for fishing and floating.

But this summer, Bugni retrieved the Montana Coalition for Stream Access buttons, handing them out to some of the dozens of people who descended on the Ruby River in southwestern Montana last month to reassert the public's right to be on the water.

They rafted about 10 miles, passing through private land where access to the Ruby is under dispute -- some fishing lodges advertise the Ruby as a ''private river" -- even as the stream access law marks its 20th anniversary.

Reduced to its simplest, the statute says that even where they flow through private land, Montana's rivers and streams are open to all if reached from public property; the land between the normal high-water marks belongs to the public. The law has been challenged in court with little success and continues to provide fodder for politicians.

Stream Access Float Day, which took place peacefully, was intended to show that disputes still surface regularly.

''Some people think they own the streams," Bugni said.

Critics say the law, on the books since 1985, violated private-property rights, increased streams' risk of environmental damage from heavy use, served the special interests of commercial fishing guides and hurt landowner-sportsmen relations.

The law that Bugni and others helped bring about in the 1980s put Montana out front in the West on the issue of access to natural resources, access that some people cite as the very reason for living in the state, known for extraordinary fishing and hunting.

''Montana is truly the last best place, not only because of our landscapes but because of what we're allowed to do on that landscape as citizens of this state," said J.W. Westman, a Park City oil company worker and avid fisherman.

But not everyone sees the law as a good thing, including landowners who have streams running through their property.

''There wasn't anything constitutional about it," said Lowell Hildreth of Dillon, who owned Beaverhead River property when the stream-access law took shape and was named in one of the lawsuits that gave rise to it.

One of the high-profile ongoing disputes involves the Bitterroot Valley's Mitchell Slough.

Landowners, among them 1980s rocker Huey Lewis, say it is a private irrigation ditch made hospitable to trout through costly restoration that landowners financed. Access advocates, with the Montana Department of Fish, Wildlife and Parks on their side, maintain Mitchell Slough is a public stream. About 50 participating in a 2003 ''fish-in" were led to the barricaded water by a legislator and a retired justice of the peace with an emphatic, ''Let's do it!"

Access disputes happen all over the country, even in states with strong laws, said Eric Leaper, executive director of the Colorado-based National Organization for Rivers.

''People say, 'Well, that doesn't apply on this little river,"' said Leaper, who calls Montana's law one of the more commendable.

''Whether it's the best in the country we should be better able to evaluate after we have all 50 of them lying in front of us," he said.

Montana's law gives people the right to use streams up to the normal high-water mark. Since Montana stream levels fluctuate a great deal each year with spring snowmelt runoff, that means that for most of the year there are dry channels and banks, and sand and gravel bars, that legally are public land.

Some anglers and others obtain permission to cross private property so they can get to streams. But a popular alternative is to reach a stream from a public access point -- often a bridge along a public road.

That alternative is at the heart of another high-profile dispute on the Ruby River, involving Atlanta businessman James C. Kennedy. He owns about 3,200 acres along the prized trout stream and last year filed a lawsuit challenging access from bridges.

Hildreth said the stream law has increased trespassing and heightened tension between sportsmen and landowners, some of whom become more protective of their property by placing new restrictions on its use.

''You stop and think, 'If they're going to take my stream bed, I'm going to protect what I can,"' he said.

Another critic, Martinsdale rancher Jack Galt, said he has not experienced problems with trespassers but still believes ''there are still some bad things about that law."

Landowners should have a say about access because often they pay taxes on stream beds, said Galt, a member of the Legislature when it passed the stream law in 1985. He opposed the legislation while it was pending, and after its passage he filed a court case charging the new law was overly broad.

Galt won some restrictions on public use of stream beds. Provisions the court struck down included an overnight camping clause and a requirement that landowners be responsible for constructing portage routes. But the core of the law stood.

In 2003, the U.S. Supreme Court refused to hear a case in which the Mountain States Legal Foundation challenged the law on behalf of Montana landowners claiming their private-property rights were violated. A federal judge in Helena had found the stream law constitutional and dismissed the case.

The first major legal battle over stream access came in the late 1970s, after Bugni and some other people from the Butte area raised the possibility of litigation and retained lawyer Jim Goetz of Bozeman to pursue it.

''I grew up in Ennis and as a kid, my brother and I used to float down the Madison in an old Army surplus rubber raft," Goetz said. ''This was in the '50s. Nobody ever questioned the right of people to float down the river."

Goetz's clients prevailed in two cases. One involved the Dearborn River, where the late D. Michael Curran of Wolf Creek disputed access, and the other the Beaverhead, where anglers had a quarrel with Hildreth.

In 1984, the Montana Supreme Court held the public is entitled to use streams capable of supporting recreational activity, and the following year the Legislature put the access law on the books.

Westman finds the stream law always facing a challenge, but he sees ''a constant rising of the citizenry to combat that."

''I think we should have cake and ice cream and punch to celebrate" the law, Westman said. ''We should celebrate ... every day of the year."

On the Net:

Department of Fish, Wildlife and Parks: http://fwp.state.mt.us