DES MOINES, Iowa >> It’s midday and the white bucket balanced on the rocky shore at Mountha Uppasay’s feet holds five or six white bass, moving sluggishly in the water she scooped from the Des Moines River.

She and her husband, who are immigrants from Laos, have been fishing since shortly after dawn and plan to catch enough to make a tasty stew to share with their children and grandchildren. Asked about possible health issues with the fish, Uppasay flashes a surprised look and says, "They’re all safe."

She’s right, to a point. The bass are nutritious, but they probably contain mercury, a toxic substance especially harmful to pregnant women and children that collects in varying levels in most fish throughout the country. Limiting consumption, particularly for those in the higher risk groups, is recommended.

Uppasay’s lack of awareness appears to be shared by many anglers who fish in rivers and lakes near urban areas, and it illustrates how many government-issued health warnings about fish fail to reach those who most need to hear them: low-income families and immigrants, some of whom fish daily or weekly for their family meals.

Most health advisories are posted directly on packages, like tobacco and alcohol, or displayed on billboard or TV ads. Iowa, like most states, posts information on its websites, and that’s where the warnings stop.

"People are starving for information," said Joanna Burger, an ecologist at Rutgers University who has worked in several states to help minimize the problem. "People want the information, but they want to be given it in a way to make their own risk decisions."

Mercury, which occurs naturally in fish, seeps into waterways everywhere, with some local hotspots scattered across the country linked to coal-burning power plants, old mines or industries.

Studies show that up to 10 percent of women of child-bearing age have mercury levels that exceed federal standards. Mercury can be devastating for the neurological development of fetuses and children. For adults, longer-term problems include vision loss and difficulty walking.

The U.S. Environmental Protection Agency says adults can eat as much as they want of some fish, but for many species the agency recommends only a serving or two a week, less for pregnant women or children. The stricter limits are suggested for predator species like white bass — fish that eat other fish — and older, larger fish more likely to exceed 0.47 parts of mercury per million.

Environmental officials agree that immigrants and low-income people dominate many urban riverbanks and lakes where fish are likely to have higher levels.

Tong Vang, who works as a community liaison in Minnesota, said Southeast Asians in the upper Midwest are especially devoted to fishing and have an affinity for white bass, a fish similar to kinds they ate in their homeland.

Vang said he thinks many in the community have not heard the warnings or don’t take them seriously.

"Some people are stubborn," Vang said.

Though mercury levels can vary, some of the most popular fish in a region can be the riskiest.

In Pennsylvania, fishermen line the banks of the Susquehanna River near York, where a top attraction is flathead catfish that can grow to 50 pounds or more.

Michael Helfrich, leader of a conservation group on the Lower Susquehanna, said he sees many immigrants casting lines.

"They don’t understand that bigger is not better," he said.

On Alabama’s Coosa River, volunteers have been interviewing anglers to learn how often they fish and what they catch. In an area with double-digit poverty levels, people rely on largemouth spotted bass and catfish, both predator fish, and other varieties for dinner.

"A lot of people have no idea that there is any kind of contamination in fish," said Justinn Overton, executive director of the Coosa Riverkeeper conservation group. "It just breaks my heart. The river is part of our community in Alabama."

Experts don’t want to discourage people from eating fish, which contains omega-3 fatty acids that are beneficial for the heart. Still, they believe governments should do more to inform anglers about simple ways to lessen dangers. Popular low-risk fish that can be eaten frequently include sunfish, crappie and perch.

In California, especially San Francisco Bay and parts of the Sacramento River, health information is being posted in fishing areas. Parks officials in Akron, Ohio, are explaining guidelines at Asian community events and circulating advisories in four languages.

"We want people to come to the park. We want people to fish," but to understand health guidelines, said parks director Mike Johnson.

But word hasn’t arrived yet for many Hmong immigrants who frequent the Des Moines River.

On this steamy summer day, several dozen anglers toss lines into the water while their families relax on blankets shaded by trees behind them.

Boun Lovan, who works for a marble installation company, said he fishes for white bass and walleye two or three times a week. For him and his family, the more he catches, the better.

"A lot of people like fish better than red meat," he said.