In the Argentine city of San Nicolas de los Arroyos on the Parana River, two huge murals reflect local concerns about a growing environmental issue for the region - the declining levels of the waterway.

The two 40-meter-high (130-ft) paintings on the sides of buildings in the city center were spurred by the artist's desire to stir debate over the river's decline. Hit by a lack of rainfall upriver in Brazil, this year the Parana reached its lowest level in almost 80 years.

One mural shows a boy extracting a native flower from the river, while the other depicts a girl whose image is reflected in the water.

"When I came to San Nicolas I was struck by the historic low level of the Parana River," Argentine muralist Martin Ron, who has created hundreds of murals around the world, told Reuters.

"These characters that I use always interact with an aspect of the place in the context where I paint and it seemed appropriate to portray this ecological message related to the decline of the Parana."

The river, which begins in Brazil before snaking through Paraguay and then Argentina to the ocean, carries some 80% of Argentina's farm exports of soy, corn and wheat, taken in giant Panamax ships from inland farm reGIONS. It is key to the country's economic wellbeing, as well as creating an important wetland ecosystem near the river delta.

The low levels have seen ships forced to take on smaller loads to sit higher in the water, hindering trade and hurting what is usually a competitive advantage for the country - the deep waterways that allow access for big container vessels.

Ron said his art was meant to play an active role in encouraging people to look at what needs to change.

The 40-year-old artist paints between 10 and 12 murals every year and has morphed his style from urban surrealism to what he calls "magical hyper-realism." Other murals he has done include a girl building with Lego blocks and a portrait of soccer player Carlos Tevez.

Although Ron spends much of his life on cranes and scaffolding, the artist confesses he suffers vertigo.

"There's a somewhat love-hate relationship with how I do my work because ironically I am very afraid of heights," he said. "So in each project it is like I have three days in which I have to acclimatize to the altitude."