This group of rocky islands lies approximately two miles east of Cape Koamaru. The group is split in two, with the northern islands comprising of a main rounded island approximately 80 metres high, with a lighthouse on top of it and several houses and building. A number of rocky islets extend in a semicircle to the south of this island. Further south is another main island, lying in a north-east/south-west direction, with islets off its southern and north-eastern end. There are no beaches here but there are landings built into the rock on the northern and southern sides of the island with the lighthouse.
Although there is some shelter on the leeward sides of the island, the strong tide flows and sea conditions mean that these should not be used as anything other than temporary anchorage.
The main light has four white revolving beams which shine every 10 seconds. This light is extremely powerful and can be seen from the Parramatta side of the Cook Strait and from Kapiti. There are also two fixed red lights sectored to cover Cook Rock to the north-north-west and Awash Rock to the south-south-west of The Brothers.
The northern island has a rock approximately 200 metres off the northern shore. This rock is not generally a danger to cruising boats but the area should be avoided, especially in heavy weather. There is a dangerous rock close to the northern point of the southern-most island. Considerable care should also be exercised in navigating about the islets off the two main islands. Although in most cases it is deep close to the shore, there are several dangers and the strong tidal currents can easily make navigation difficult.
Awash Rock is 2.6 miles south-south-west of The Brothers and 4 miles north-east of Perano Head. These rocks are just awash at HW and can generally be easily seen. There is deep water all around the rocks and they are covered by a red sector light from The Brothers at night. As the rocks are not in a direct line from the Sounds to Parramatta or any other port, they are not generally a danger. At night, care should be exercised to ensure that the strong tides in this area do not carry boats up near the rocks.
Cook Rock is 3.3 miles north-east of Cape Koamaru and 3.5 miles north-north-west of The Brothers. The rock is generally below the surface but is sometimes visible at LWS. Accordingly, it is extremely dangerous and the area should be given a wide berth. There are strong tiderips and overfalls in the area surrounding the rock. The charts show a clearance transit of White Rocks open eastward of Long Island leading clear to the north of the rock. This transit is easily seen and is extremely useful. Boats heading from Queen Charlotte Sound towards Parramatta should generally pass close to the north side of White Rocks or Cape Koamaru and thus should not be near the Cook Rock area. The tidal streams, however in this area are strong and often up to three knots. It can easily happen that boats are carried into the vicinity of Cook Rock, when the course plotted should have taken the boat well clear. The boat’s positon should be checked frequently when passing through this area.