A method for monitoring properties of an aqueous stream online in a pulp, paper or board manufacturing process, the method comprising - providing an initial aqueous stream originating from said process, the aqueous stream containing solid matter exhibiting a first settling behavior; - adding modifying agent to the initial aqueous stream at an addition rate sufficient to provide a modified aqueous stream containing solid matter exhibiting a second settling behavior different from the first settling behavior; - conducting a sample of the initial aqueous stream or modified aqueous stream, any combination stream comprising the modified aqueous stream or any substream of the modified aqueous stream batchwise from a sampling point to a settling vessel having a volume; - allowing the sample to settle in the settling vessel and simultaneously measuring the settling behavior of the solid matter in the sample locally in the settling vessel as a function of time; - depending on the determined settling behavior of the solid matter in the sample changing the addition rate and/or type and/or addition point of the modifying agent, characterized in that the settling behavior is determined by determining in NTU/s the settling velocity of said solid matter by measuring the turbidity of the sample locally in the settling vessel as a function of time during the first 180 seconds of settling, allowing the sample to further settle in the settling vessel and after that determining in NTU the settled turbidity of the sample, based on the determined settling velocity of the solid matter in the sample and the determined settled turbidity of the sample, adding the modifying agent at an addition point of the manufacturing process in an amount sufficient to maintain the settling velocity below a predetermined level, the method comprising determining the settling velocity in NTU/s and the settled turbidity in NTU, by measuring turbidity using electromagnetic radiation in the range of UV, visible or IR wave lengths from an electromagnetic radiation-based detector, wherein said process is a paper making process and said sampling point is located in an aqueous circulation stream of a paper or board machine, preferably in the white water line of the paper machine, or wherein the sampling point is in the feed line of pulp or broke to a paper or board machine. - providing an initial aqueous stream originating from said process, the aqueous stream containing solid matter exhibiting a first settling behavior; - adding modifying agent to the initial aqueous stream at an addition rate sufficient to provide a modified aqueous stream containing solid matter exhibiting a second settling behavior different from the first settling behavior; - conducting a sample of the initial aqueous stream or modified aqueous stream, any combination stream comprising the modified aqueous stream or any substream of the modified aqueous stream batchwise from a sampling point to a settling vessel having a volume; - allowing the sample to settle in the settling vessel and simultaneously measuring the settling behavior of the solid matter in the sample locally in the settling vessel as a function of time; - depending on the determined settling behavior of the solid matter in the sample changing the addition rate and/or type and/or addition point of the modifying agent, characterized in that the settling behavior is determined by determining in NTU/s the settling velocity of said solid matter by measuring the turbidity of the sample locally in the settling vessel as a function of time during the first 180 seconds of settling, allowing the sample to further settle in the settling vessel and after that determining in NTU the settled turbidity of the sample, based on the determined settling velocity of the solid matter in the sample and the determined settled turbidity of the sample, adding the modifying agent at an addition point of the manufacturing process in an amount sufficient to maintain the settling velocity below a predetermined level, the method comprising determining the settling velocity in NTU/s and the settled turbidity in NTU, by measuring turbidity using electromagnetic radiation in the range of UV, visible or IR wave lengths from an electromagnetic radiation-based detector, - depending on the determined settling behavior of the solid matter in the sample changing the addition rate and/or type and/or addition point of the modifying agent, based on the determined settling velocity of the solid matter in the sample and the determined settled turbidity of the sample, adding the modifying agent at an addition point of the manufacturing process in an amount sufficient to maintain the settling velocity below a predetermined level, the method comprising determining the settling velocity in NTU/s and the settled turbidity in NTU, by measuring turbidity using electromagnetic radiation in the range of UV, visible or IR wave lengths from an electromagnetic radiation-based detector,