Marbellup Brook is located 13 kilometres west of Albany. The average annual rainfall across the catchment is 1100mm and the majority of the rainfall occurs over the winter months.

The upper Marbellup Brook catchment consists of a low forest of Jarrah and Sheoak. The floodplain mainly consists of sedgeland. Since European settlement approximately 80% of the catchment has been cleared for agriculture.

Originally the Brook would have flowed in Lake Powell before overflowing in Lake Manarup and Torbay Inlet. Artificial drainage that was constructed across the catchment in the 1950s, directed the flow away from Lake Powell and straight into the Inlet.

The Marbellup Brook was sampled between May 2006 and September 2007.

No fish data was recorded for the Marbellup Brook.

Sites MAR03, MAR04, MAR09, MAR10, MAR11, MAR14, MAR16, MAR24, MAR26, MAR27 and MAR29 were all considered to be in a pristine condition (A grade). MAR13, MAR15, MAR17, MAR21, MAR22 and MAR26 were in a slightly degraded condition and were in B grade condition. All other sites were in a degraded or severely degraded condition.

Water samples were taken once from each site so while they help describe the water quality at the time of sampling they can not be used to explain the overall condition of the river for the rest of the time. The water quality parameters across all sites have been averaged to determine an overall condition.

The Marbellup Brook is a fresh water and neutral system. The Brook recorded very high average levels of turbidity (50.4 ntu), total nitrogen (1731μg/L) and total phosphorus (266μg/L) across the catchment.