The part of "Heizelbeek" that the press release talk is the north part of V4 of the pond : https://osmlab.github.io/osm-deep-history/#/way/38790441

coordinationsenne say that's the stream doesn't exist anymore and there is a lot of information here : https://document.environnement.brussels/opac_css/elecfile/STUD_2019_ParcSobieski

https://geodata.environnement.brussels/client/bruwater/index/ground/station show the old situation of culvert that supplies water to some pounds. 

One of the new acess is here : https://www.mapillary.com/app/?pKey=307104335205602