The Maroondah Reservoir, with its distinctive Classically-inspired outlet tower and dam wall, represents the first of three major water supply reservoirs constructed by the MMBW during its second major phase of development during the 1920s and 1930s. It is of regional significance.

The dam wall is a distinctive example of early engineering techniques, with its gravity arch design and Cyclopean rubble concrete construction.

The construction of the dam wall represented an important advance in the technology of dam-building, utilising bi-cable aerial ropeway and travelling aerial cableway, the same system later used in the construction of the Silvan dam in 1927-31.

The reservoir, and the associated reservoir park, together comprise one of the most popular and enduring tourist destinations for day trips from Melbourne, providing generations of visitors with views of the natural forest catchment surrounding the reservoir and the landscaped gardens within the park. (McCann 1993: 71)

The park represents the MMBW's success in maintaining a closed catchment policy whilst developing a place for popular recreation, in keeping with the established recreational traditions of the Healesville-Black Spur area. (McCann 1993: 75)

The Maroondah Catchment is the only closed catchment in the Melbourne Water system to allow public access via the Maroondah Highway and walking tracks. (McCann 1993: 71)

The Maroondah dam consists of a gravity arch, Cyclopean rubble concrete wall, extending to a total length of 946 feet along the top. It is 135 feet height at the highest point, and a maximum thickness of 101 feet at the base. Compared with the Board's other storage reservoirs, the Maroondah dam is an unusually elongated structure. The dam has a distinctive concrete walled walkway along the top of the curved dam wall, featuring large concrete pillars and sections with oblong holes. Circular cuts in the walkway floor represent cores cut vertically into the dam wall in 1989 in order to sink steel tensioning cables into the rock base of the wall. This was part of remedial work undertaken at that time, including the enlargement of the spillway. A section of one of the cores removed from the wall is located near the walkway entrance, and illustrates some of the smaller "plums" (large pieces of rock) that were set into the concrete during the dam's construction. An inspection tunnel traverses the interior of the dam wall for most of its length, and vents (added later) indicate the extent of the tunnel near the top of the wall.

Two recently restored brass plaques mounted on the entrance pillars to the walkway commemorate the construction of the dam between 1920 and 1927. The walkway along the top of the dam wall leads to a new bridge over the concrete spillway, expanded to three times its original width in 1989 to allow for peak flood conditions. The natural rock wall on the eastern side of the spillway remains in its original condition, while the natural rock section of the lower end of the spillway (visible from the Reservoir Park below the wall) has also been widened since first constructed. The original section of rock is distinguishable because it forms a U-shape, unlike the recently-cut straight section of rock. A plaque and time capsule were set in the base of the wall in 1991 during the centenary celebrations for the opening of the Watts River Diversion Weir and Aqueduct system. It is to be opened in 2041.

The equally distinctive outlet tower is located in the reservoir near its northern perimeter, visible from the dam wall. It is a circular domed structure in Classical style featuring columns with capitals, and set on a circular concrete base. An arched bridge connects the tower with the land, and an entrance arch at the entrance to the bridge continues the Classical theme. The reservoir receives inflow from a total catchment area of 14,680 ha, plus the Grace Burn Creek diversion weir via a channel to Lindupp's Basin and siphon. (McCann 1993: 71-72)

The Reservoir Park occupies about 2 ha at the base of the Maroondah dam wall and spillway. It consists of a series of curvilinear roads and pathways down the side of the valley from Maroondah Highway, through formal garden and lawns to the flat valley floor utilised for carparking and picnic facilities. There are several distinctive features in the park.

- A natural manna gum "forest" covering about 0.5 ha is located on the northern bank of the Watts River, near the base of the spillway.

- The "rose steps" is a set of concrete steps leading from near the base of the Maroondah dam wall up the embankment to a higher terrace. The stairway is currently lined with pencil pines, although the park management plan recommends replacement with standard rose bushes as originally used.

- Two domed concrete valve houses are located near the base of the dam wall. The hydraulically-operated valves provide for the control of water flow from the reservoir into the Watts River if necessary, and are associated with a compensation channel lined with stone pitchers (no longer in use). The compensation channel now used is called the "lily pond", and is a depression resulting from scouring which occurred when the valves were opened at one time. The released water flows back into the Watts River at this point. A foot bridge provides access over the compensation channel to the viewing point at the base of the spillway.

- A sundial consisting of "MMBW" and Roman numerals I to VII with a central pole is located adjacent to the valve houses at the bottom of the dam wall. It has been designed without the number VIII, apparently because the location of the dial does not allow sunlight to penetrate at that time. A weathercock on top of the pole has been dismantled because of vandalism. (Lindsay Bergin: pers. comm.) The clock is best viewed from the walkway along the top of the dam wall.

- Two rotundas constructed between 1946 and 1948 are located in the park, one near the base of the slipway, and the other near the kiosk along McKenzie Avenue. They employ a central upright support with poles radiating from the centre to form the roof structure, and upright poles supporting the roof around the perimeter. The upright poles supporting the roof around the perimeter. The upright supports and roof timbers were cut from nearby trees, and the original split timber shingles have been replaced with treated pine shingles.

- A caretaker's house, constructed in red brick, is located at the eastern end of the park, fenced off from the park and in its own garden setting. Two toilet buildings along McKenzie Avenue are constructed of similar materials.

- The form plantings of exotic trees and shrubs line the main entrance driveway (McKenzie Avenue) and extend over the lawns to the base of the dam wall. In the western half of the park, indigenous trees tend to predominate. The introduced species include Californian Redwood and Oregon trees, presumably dating from the period after the dam's construction (1927). A eucalyptus tree, planted by the Governor, Sir William Slim in c. 1950, stands next to the Californian Redwood near the "rose steps". Some of the pathways and the stone edging and guttering along the pathways at the base of the dam wall were laid in the 1946 to 1948 period.

- The entrance gates, roadway and perimeter fence form distinctive elements of the park. The gates are of wrought iron and "Maroondah Dam" is shaped in iron above the gate. McKenzie Avenue curves through the lawns and formal plantings down the valley slope to the main visitors' facilities near the bottom of the valley. The fence almost encircles the Reservoir, and features concrete posts with barbed wire. Some of the original posts remain, featuring an indented section recalling the concrete pillars along the dam walkway. The replacement posts are plain. The fence most noticeably defines the boundary of the park along the Maroondah Highway. (McCann 1993: 75-76)

Physical Conditions: Good

Integrity: Minor Modifications