It has long been stated that Isaac Watts did not paraphrase this psalm. This in incorrect. He simply did not include it in his Psalter. It appears in
Reliquiae Juveniles (1734) with the comment, "Had Horace or Pindar written this ode, it would have been the endless admiration of the critic, and the perpetual labor of Rival translators; but 'tis found in the Scripture, and that gives a sort of disgust to an age which verges too much toward infidelity. I could wish the Muse of Mr. Popе would choose out some few of these pieces of sacred Psalmody, which carry in them the more sprightly beauties of poetry, and let the English Nation know what a divine Poet sat on the Throne of Israel...This particular Psalm could not well be converted into Christianity, and therefore it appears here in its Jewish Form: The vengeance denounced against Babylon."
Maybe this should make an appearance in modern editions of Watts's Psalms...
Here is the full text, with modernized spelling:
When by the flowing brooks we sat,
The brooks of Babylon the proud;
We thought on Zion's mournful state,
And wept her woes, and wailed aloud.
Thoughtless of every cheerful air,
(For grief had all our harps unstrung)
Our harps neglected in despair,
And silent on the willow hung.
Our foes who made our land their spoil,
Our barbarous lords, with haughty tongues,
Bid us forget our groans awhile,
And give a taste of Zion's Songs.
How shall we sing in heathen lands
Our holy songs to ears profane?
Lord, shall our lips at their commands
Pronounce Thy dreadful name in vain?
Forbid it Heaven! O vile abuse!
Zion in dust forbids it too :
Shall hymns inspired for sacred use
Be sung to please a scoffing crew?
O let my tongue grow dry, and cleave
Fast to my mouth in silence still,
Let some avenging power bereave
My fingers of their tuneful skill,
If I Thy sacred rites profane,
O Salem, or thy dust despise;
If I indulge one cheerful strain,
Till I shall fee Thy towers arise.
'Twas Edom bid the conquering foe,
Down with Thy towers, and raze Thy walls:
Requite her, Lord: But Babel, know,
Thy guilt for fiercer vengeance calls.