Dam House is seen here, standing at the south end of the weir.
Foundations of Holgate Wall in the old postcard can still be seen today on the ground surface by the track, plus a few low sections in Holgate Lane itself. The large tree behind still stands in 2009, but is now old and decayed.

All that is left of Dam House in 2009. Only the basement remains. It is thought that the upper level, now gone, was at one time the ferryman’s house, who also looked after the salmon ‘hecks’ or traps. The part you can see may originate from an earlier phase of use and, though ruined, might be one of the earliest remaining buildings from Boston Spa’s past..

Inside there are interesting details hinting that its function involved the use or management of water. The photograph on the left shows symbols carved in the stone about 90cm up one of the inside walls. Was it used to mark a required depth?

There is also the shallow impression of an old leat leading towards it from a notch in the river bank 50 metres upstream. This could have provided a head of water into the building through an arched culvert, controlled by stop boards fitted into vertical stone slots, lined with iron. Remains of these are still visible just to the left of the ruler.
 

Above left is a plan of the site drawn in 2009, with the shallow leat running towards Dam House and to the right part of the 1963 OS map.

Eric Matthews, a building archaeologist who has made a study of the linen industry, has inspected the site.

As a result we do not think it was some kind of mill, as it was too small and close to the weir.
Eric thinks that this basement area provided  stone tanks used for flax retting, possibly in the eighteenth century or even earlier.

Retting was one of the stages in preparing the flax for the mill. It involved a slow process of steeping, softening and rinsing the raw flax plants in water to make it easier to get at the fibres they contained.

There was flax milling in Clifford where the Grimston brothers had their mill.  They also owned a linen  mill and flax retting site on the River Ure at Mickley near Masham, which  according to Eric is similar to Dam House.

Some people tell of it being used for keeping caught salmon in running water under the fish keeper’s house. It is possible that it was used in that way following the decline of the local linen industry in the nineteenth century after flax retting had ceased.
 

More investigation and recording are needed.  Some protective measures are urgently required to protect against further erosion and undercutting of  the river bank.  The enlarged plan above shows how much the riverbank has eroded since 1963.  This has led to the creation of a large back eddy current when the river is in flood.  This is cutting back the bank behind the building and stones are collapsing into the river as shown in the pictures below.

Rural industries including mills have been an important part of our local history for centuries.  In many cases the same sites have been used for different purposes at different times. 

Here the Ferryman's House may have been built over the earlier structure.  Or the upper storey might have existed before to store flax and it was changed into a dwelling.

An old postcard view dominated by Thorp Arch Mill on the opposite bank. Dam House is just visible in the trees to the left of the weir.

The mills to the right are another example of how sites have evolved from medieval through to modern times by changing their function to suit local needs and industries.