The answer lies in the meeting of 1999 ...

"...It is therefore proposed that the portion of Lot Pt 11 currently reserved as Public Open Space be zoned to Residential “B” (R30) in accordance with the surrounding land in order to remove the boundaries between zones and thus provide flexibility in the ultimate subdivision design. The area finally set aside for recreation purposes shall then be reserved when the subdivision has occurred.

In this regard it shall be noted that the normal subdivisional process is for land vested with the local authority for recreation purposes to be reserved by way of an omnibus amendment to the Scheme after the subdivision has occurred and thus the precise boundaries of the recreation reserve defined. The above would in no way relinquish the developer from the obligation to provide the normal public open space land area..."

from the minutes of the meeting in 1999

So way back then it was decided that the boundaries would be defined once the development had occurred, they would change the zoning of the area, meanwhile we are given the opportunity to comment, after the event? Well to bad if I was to say "no don't do it, it will kill the lake and wildlife will disappear", but wait it has, what is the point, the developer was given license to develop and use whatever portion they deemed necessary, now the development is right on top of the lake/drain, there is no buffer zone around it and the damage is done!

This amendment is really just about the zoning of the R80 section, the modifying of the boundary of the Local Open Space has been done, it's too late to comment on that.