"We began repatriating the illegal immigrants last month [October] with their livestock as the trend was likely to create a serious environmental crisis in the area," Mlingwa said on Tuesday during a parliamentary session in Dodoma, the country's political capital.
The immigrants, estimated by the government to number at least 100,000, moved into grazing land in Kagera, bringing 42,550 cows, 8,920 goats and 2,100 sheep, he added.
So far, Mlingwa said, 50 immigrants, 3,295 cows and 70 goats had been repatriated. However, he said the exercise was cumbersome as it was difficult to identify illegal immigrants from the local people because they have "similar characteristics".
Mlingwa was responding to a legislator from Kagera Region, Gosbert Blandes, who wanted know why illegal immigrants had been allowed into the country with large herds of cattle.
Blandes said the region, particularly Karagwe District, was already saturated with livestock as it had 145,318 cattle, 79,053 goats and 4,619 sheep.
However, Mlingwa partly blamed Karagwe residents for the problem, saying there were cases where they gave shelter to the foreigners or gave false information to government officials.
An official with the Tanzania Fisheries Research Institute, Joyce John, told IRIN that over-grazing around Lake Victoria was contributing to the adverse effect on the eco-system of the world's second-largest lake.
"Over-grazing and cultivation in the Lake Victoria basin is a serious problem and there is a need for a concerted effort to solve the problem," she said.
Apart from illegal immigrant pastoralists who have invaded grazing land around Lake Victoria, the government earlier in the year expelled some local livestock keepers from riverbeds in southwestern Tanzania's Usangu Basin.
"The livestock keepers had moved thousands of cattle into the basin, which is the main source of water to rivers that lead to dams which feed hydro-electric power generators downstream," John Mwakipesile, the regional commissioner of southwestern region of Mbeya, said.
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