Well, the brick is not initially taking up any space in the water so once it is thrown in the water the water will rise. However as the weight of the brick is removed from the boat the boat will rise slightly out of the water therefore counteracting any reducing/ removing of a rise in water levels. Therefore any changes in water level will be dependant upon the density of the brick.

When the brick is in the boat, the displaced water floating the brick is equal in weight to the weight of the brick.

Because the brick sinks when thrown into the lake, the water it displaces weighs less than the weight of the brick.

Therefore, the level of the lake drops since less water is displaced when the brick is in the lake.

When throwing the stone the water level drops as if one would remove an amount of water with the same weight as the stone. When the stone is submerged, the water level rises again as if one would add a likewise volume of water. The shoreline will change, and the begin and end situation will also be different, if given the fact that the density of the stone is not equal to the density of water.

I'm pretty confident that this is the correct answer. According to Wikipedia:

In the case of an object which sinks the amount of fluid displaced will be equal in volume to the immersed object, whereas in the case of an object which floats the amount of fluid displaced will be equal in weight to the displacing object

[http://en.wikipedia.org/wiki/Displacement_(fluid)]

When the brick is on board the boat it contributes to the overall weight of the boat, which will cause the boat to displace that weight of water. When the brick is submerged it can only displace its volume of water, and if the brick is more dense than water then its volume will be smaller than if it displaced its entire weight's worth. So if the brick sinks then the level of water will go down but if the brick is made of pumice then the level of water will stay the same.