Firstly, let me present the flag of the province:
The history starts in 2009, when a contest was made to select the new flag of the province, that was until flag-less.
According to the author, the symbolism of the design is the following: blue stands for justice, and the rivers and lakes, green for hope and the agriculture, the forests and the valleys; white was chosen because it's formed by the union of all the colors; the black canton with thirteen stars represents the thirteen departments (a geographic subdivision) that forms the province. The use of the black color is unclear, but my theory is that it's someway allusive (canting) to the name of the province, that means "black river" in Spanish.
Soon after the flag was designed, many negative critiques appeared, specially with the opinion that black was improper because of its association with mourning. Particularly, I think the flag isn't bad, I only think that black and blue shouldn't be put together because of their similarity.
Graver of the accusations of plagiarism. Firstly, that it was very similar to the flag of the former Kingdom of Araucanía and Patagonia. The kingdom was an attempt, by a French adventurer, to establish a monarchy on southern Argentina and Chile (including part of current Río Negro province) with the support of native Mapuche people, but severely combated by Argentinean and Chilean armies. A more serious claim of plagiarism is related to an unofficial flag that, according to Wikipedia, was used on some deeds by province government. The colors, the stars, all the elements of current flag are there!
Usually, looking for symbols on its own history (is it really self-plagiarism) is not unethical (if you cite the sources, obviously), but is it fair appropriating of someone's work to gain a contest?
What's your opinion about it? Your comment is welcome!