Large-scale works began in the Danube Delta as early as the second half of the 19th century. First corrections of the Sulina arm began in 1862, and they continued throughout the 20th century. As a result, the length of the Sulina arm was reduced from 92 to 64 km, and its flow more than doubled, thus making it suitable for large-vessel navigation. Correcting the six large meanders on its course thereby reduced the length of the Sfântu Gheorghe branch from 108 to 70 km, and its flow also increased somewhat. Both these increases were made to the detriment of the Chilia arm, which at present remains the most unspoiled arm of the main three. These corrections, as well as the digging of various secondary channels throughout the body of the delta, have had a serious impact on the ecosystem. Natural environments have been altered, the breeding pattern of fish has been disrupted, and the flows in the main arms have increased, with serious consequences regarding the discharge of alluvia and the erosion of banks.