Both will make the water level of the lake lower
Until they are on the boat they shift a volume of water equal to
$(weight\ of\ the\ brick)\ /\ (density\ of\ the\ water)$.
When they are thrown into the lake they shift a volume of water equal to the volume of the brick, that is
$(weight\ of\ the\ brick)\ /\ (density\ of\ the\ brick)$.
Given that iron and gold have higher density than the water, the volume shifted is less.
To be more complete, given the densities of gold and iron respectively $19.30 g/cm^3$ and $7.87 g/cm^3$ if:
$l1$ = level of the water lake with both the bars on the boat
$l2$ = level of the water with iron brick on the boat and gold brick into the lake
$l3$ = level of the water with gold brick on the boat and iron brick into the lake
$l4$ = level of the water with both bricks into the lake
$l1 > l3 > l2 > l4$