This was a four mark practise question answer that I received full marks for. Hope it helps.
Discuss how the Tasmanian Dams Case shifted the balance of law-making power between the states and the Commonwealth.
The Tasmanian Government intended to dam the Franklin River in the 80s, however Commonwealth got intervened; having signed an international treaty committing the Commonwealth to protecting world heritage sites, it then passed laws protecting the Franklin River and surrounding areas from any development. The issue was whether the Commonwealth law was valid. Tasmania believed that the Commonwealth had entered into its area of law-making responsibilities. Tasmania argued that the specific powers in section 51 of the Constitution did not give the Commonwealth the power to make such laws about the environment. The High Court decided that the laws were valid because the "external affairs" power (section 51 part 29) power in the Constitution gives the Commonwealth the ability to enter international treaties and pass laws that give effect to those treaties. The external affairs power allows the Commonwealth to pass laws on any matter within a treaty it has signed, even if that law then enters into the states' residual powers. The broad interpretation of the external affairs power significantly increases the law-making powers of the Commonwealth at the expense of the states. Commonwealth's law making power is seemingly endless because they can now make laws about anything that is covered by exclusive powers, concurrent powers and anything under a treaty (even residual).