Erm, just in case?
In My Opinion it was a process of elimination. Police often search Lakes, Rivers and Scrubland when they have no real idea if a missing person is alive or dead.
This should have been done by The Portuguese Police in the beginning. It wasn't. And now we know that Madeleine isn't buried there.
The Portuguese Police carried out thorough searches in PdL, and the Scrubland was screened by Eddie too;
The teams available and deployed by Major Seqeuira were drawn from unit of the GNR, Civil Protection, Fire Brigade, Red Cross and Urban Police. Each team numbered around 10 and between 80 to 100 personnel were involved in search activity.
The searches were based on a strategy of searching in "rescue and recovery mode? to locate the missing girl alive or if dead, not as a victim of crime. This search phase lasted for 7 days from the date M McCann went missing.
The search was split into 3 zones radiating out from Praia Da Luz in a northward direction. The first zone extended 3km to the EN125 road at Espiche. W?hin this zone, sectors were drawn using the natural boundaries that exist and
included the entire village. Officers were briefed and debriefed before and after deployments and records of activity collected.
Each sector was repeatedly searched on 3 separate occasions over the 7 days using officers conducting line searches and supported by air scenting dogs.The next Zone 2 was extended out to a radius of 7km to the boundary of the N120 road at Bensafrim. As the sectors were larger and in order to support the line searches 2 GNR officers on motorcycles and 6 GNR officers on horse-back were deployed. These sectors were all searched on 2 separate occasions over the 7 day period.
The outer zone 3 was extended to 15km at Barragem de Odiaxere a dammed lake. This zone is in a mountainous region subject to flash forest fires.
Therefore Fire officers who routinely patrol and have local knowledge of the area were tasked to drive the tracks, visit empty properties to look for the missing girl. Additionally the fire brigade used a boat to visually inspect the surface water of the lake.
On 01-08-07 the PJ and GNR assisted by a canine, conducted searches on the eastern beach and wasteland in Praia da Luz.
On 07-08-07 the western beach and remaining wasteland areas were searched using canine and GNR personnel.
http://www.mccannpjfiles.co.uk/PJ/MARK_HARRISON.htm