This thesis analyses environmental federalism in Ethiopia with the view to examine the duty of the two levels of governments (the Federal and Regional Governments) in relation to protecting Lake Tana from Water Hyacinth. Lake Tana is the largest lake in Ethiopia and one of the ten largest lakes in Africa, and the main source of the Blue Nile River and it is registered as a biosphere reserve site by UNESCO in June 2015. Unfortunately, however, it is invaded by water hyacinth, which is deadly weed. As per Article 44 of the Constitution, all citizens shall have the right to live in clean and healthy environment and Article 92 states, the government and the citizens shall have the duty to protect the environment. Thus, both the federal and regional governments of Ethiopia are responsible to protect the natural resources of the country. The FDRE Constitution has adopted centralized lawmaking power and it grants ANRS the responsibility to administer land and other natural resource situated in the region as per the federal laws. On the other hand unlike the Constitution; the federal water resource management policy incorporates decentralized natural resource management approach. But the Ethiopian Water Resource Management Proclamation provides centralized water resource management. Thus, despite the policy recognizes IWRM, there is no well-established legal framework for the implementation of this approach in Ethiopia. Even though the ANRS have been working to alleviate Water Hyacinth infestation from the Lake, the federal government has not been involved in all its capacity to eliminate water hyacinth from the lake. In addition, there is no involvement by the international community to overcome the danger posed against Lake Tana biosphere reserve. In this regard, the research identifies legal and institutional gaps concerning water hyacinth removal effort in the Lake. In general, the technical and policy failures, lack of enforcement of policies, overlapping and conflicting roles and responsibilities between and among government institutions are examined in relation to the failure to achieve the desired conservation and protection activities in Lake Tana biosphere reserve. Finally, the research comes up with conclusion and recommendation based on the findings of the research conducted. Key Words: - Environmental Federalism, Water Hyacinth infestation, Lake Tana Biosphere Reserve