Subsequently, the Don Catchment Rivers Trust commissioned the engineers Arup Group to assess how fish migration could be encouraged. They only considered the weirs from Old Wheel to Owlerton Wheel, as the weir at Stacey Wheel is very close to the reservoir dam, and would not increase the length of river accessible to fish by very much. The two weirs below Hillsborough, at Birley Wheel and Black Wheels, are the subject of a separate study being carried out by the Environment Agency. The Environment Agency also assessed the impact on the river of removing the weir at Limbrick Wheel entirely. Arup's report considered two options at each site, from complete removal of the weir, partial removal, provision of a technical fish pass, construction of a bypass channel, easement, and the installation of a low-cost baffle system. Removal of the weir was only considered at Limbrick Wheel, and was ruled out for Low Matlock Wheel, as that is a scheduled ancient monument, and for Olive Wheel, as there is a flow measurement gauging station immediately above it. Partial removal of the weir was not thought to be appropriate in any of the cases, and only the option of easement was considered for Loxley Old Wheel. Various easement options are available, including notches and gaps, baulks, baffle systems, preliminary weirs, and rock ramps, and at any one site, several of the options may be required. Easements are generally not subject to the same rigorous technical assessment as the other options, and the process of deciding what needs to be done is somewhat subjective.