Watery Quiz answers

1) Old Father flowing softly?
Thames
2) A mutilated warrior, is she running a bookstore?
Amazon        
[Traditionally Amazons had right breast removed to allow use of bow]
3) Kipling's Great, grey-green greasy river
Limpopo        
4) Forget the waltz, from what I've seen, it's brown
Danube
5) As the old riddle has it, four "eyes" but can't see
Mississippi
6) A river that runs between two "seas" (another childhood riddle)
Thames        
(I'm a London lad, and was raised with this riddle.)
The Thames runs between Chelsea (on the North bank) and Battersea (on the South)]
7) "Up the River [River name] our troops shall Advance,
    To the Grenadiers' March, we will teach them to Dance"
    Cape Breton, we've taken...."
St Lawrence        
[From the song 'Hot Stuff']
8) The Germans wanted to set a watch here, Loraine & Thorne wanted to wind it up
Rhine        
[The traditional German song "Wacht am Rhine"/Loraine & Thorne performed "When we've wound up the watch on the Rhine" -If you never heard it, it's worth the effort to avoid it]
9) Where the Flying Cloud turned pirate, sounds like where Madrid or Barcelona get their tap water
Spanish Main
10) This river gave its name to the battle which gave the British Army its worst day Ever
Somme        
[Battle of the Somme, started 1st Jult 1916 - The British Army lost some 60 000 Killed, wounded, and prisoners on the first day]
11) Until then unbridged, at night, this river is said to be gloomy (or drumlie)
Annen Water
12) Lament of the last man to be executed for the '15 Jacobite rising
Derwentwater's Farewell        
[Earl of Derwentwater was sentenced to death in 1716 but managed to escape - returned for the '45, recaptured and executed on '16 warrant. He was beheaded in 1746]
13) (Jeff) Christie's only No.1 (1970)
Yellow River
14) According to McGuire, on the eve of destruction there are bodies floating here
Jordan
["Eve of Destruction" in the DT]
15) Site of a battle. Korea November - December 1950
    "...across frozen rivers and in temperatures down to 35 degrees below zero..."
Chosin Reservoir aka "Frozen Chosin"
[US 1st Marine Division (with attached Army units) surrounded fought its way south. "...across frozen rivers and in temperatures down to 35 degrees below zero..."]
16) Sail this in a gumtree canoe
Murray River        
[Hrothgar has pointed out that it could also be the Murrumbidgee or Tombigbee, but I took Murray from "Gumtree Canoe" in the DT]
17) For the eccentric driver, a Massachusetts town is named (indirectly) for a bridge over this river
Cam        
[Cambridge UK, Cambridge Mass]
18) An Egyptian goddess names this stretch of an English river
Isis
19) On 1st June off Boston, an Irish river captured an American Bay (one point for each)
Shannon and Chesapeake        
[HMS Shannon captured USS Chesapeake on 1st June 1813 off Boston Harbour during the war of 1812]
20) Rodgers And Hammerstein's cockeyed optimist appears here.
South Pacific        
[One of the lesser known songs from 'South Pacific"]