Lake Baikal is a unique natural object and a UNESCO World Heritage Site. At the same time, Baikal is a major fresh water inland fishing water body of Russia and the whole Eurasian continent. Extensive fishing began here in the second half of the 19th century and continued, with short-term moratoriums on commercial fishing connected with the depletion of valuable fish stocks, until October 2017, when a new ban was imposed. One of the reasons for this ban was a growing scale of illegal, unreported and unregulated fishing. In spite of restrictive measures, illegal fishing in Baikal is massive. According to statistical data provided by Chief Department of Internal Affairs in Irkutsk Region, the Ministry of Internal Affairs of the Buryat Republic, Department of the Ministry of Internal Affairs of Russia in Zabaikalsky Region and the Federal Service for Supervision of Natural Resources, the number of crimes under Art. 256 of the Criminal Code of the Russian Federation increased 45 % from 2013 to 2018. After the fishing of omul was limited in 2017, the problem of illegal fishing became a burning issue. The current measures of preventing environmental violations in this sphere are not always well-coordinated. To improve their effectiveness, it is necessary to take into account the results of a systemic monitoring of the complex of causes that determine this problem when developing new measures. The authors of the article use mathematical modeling, primarily, regression analysis, to research the factors that lead to crimes and violations of law in the sphere of fishing. The identification and research of factors determining illegal fishing of water bio-resources with the use of mathematical modeling is an element of a deeper analysis of criminological data carried out with the purpose of improving the effectiveness of counteracting illegal fishing and protection of a unique natural object - Lake Baikal.