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USGS Surface-Water Daily Statistics for Montana

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Questions or concerns about USGS data and data products in Montana and Wyoming can be directed to the Wyoming-Montana Water Science Center Data Management Section.


The statistics generated from this site are based on approved daily-mean data and may not match those published by the USGS in official publications. The user is responsible for assessment and use of statistics from this site. For more details on why the statistics may not match, click here.

USGS 05020500 St. Mary River at International Boundary


000, 95
Hydrologic Unit Code --
Latitude  49°00'41.07", Longitude 113°17'58.37" NAD83
Drainage area 462  square miles
Gage datum 4,116.04 feet above NGVD29
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00060, Discharge, cubic feet per second,
Day of
month		 Mean of daily mean values for each day for water year of record in, ft3/s   (Calculation Period 1901-10-01 -> 2025-09-30)

Calculation period restricted by USGS staff due to special conditions at/near site
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
1 162 149 157 259 878 2,440 1,950 778 474 440 386 264
2 161 150 158 259 915 2,470 1,880 756 466 446 382 264
3 162 149 157 265 954 2,540 1,850 734 465 449 377 262
4 164 150 158 275 976 2,650 1,810 709 457 451 374 258
5 164 150 160 288 1,000 2,780 1,760 683 456 450 371 253
6 164 150 161 303 1,060 2,820 1,710 658 458 454 367 248
7 163 151 162 311 1,110 2,850 1,650 642 459 451 372 241
8 161 150 162 314 1,180 2,920 1,590 634 454 451 402 235
9 159 150 164 319 1,230 2,880 1,540 624 453 448 408 229
10 159 150 173 333 1,280 2,790 1,490 612 452 446 401 226
11 155 148 177 344 1,330 2,730 1,450 601 453 443 387 219
12 152 149 176 356 1,360 2,680 1,410 586 454 440 386 215
13 150 149 177 378 1,400 2,670 1,380 574 461 438 386 209
14 150 149 177 404 1,460 2,640 1,340 570 458 436 385 205
15 151 152 179 416 1,510 2,580 1,310 565 457 433 384 200
16 150 156 185 440 1,590 2,580 1,280 555 460 433 380 198
17 150 155 187 461 1,660 2,640 1,230 544 461 438 372 197
18 150 154 193 476 1,740 2,640 1,200 535 464 442 363 194
19 149 153 198 483 1,820 2,630 1,160 523 467 437 353 192
20 148 149 216 507 1,880 2,660 1,110 514 471 434 342 191
21 147 147 226 539 1,930 2,610 1,080 513 474 430 334 188
22 147 147 226 565 2,000 2,510 1,060 510 478 423 325 186
23 148 147 224 594 2,080 2,410 1,030 507 478 416 317 183
24 148 153 218 623 2,160 2,330 992 512 479 410 315 179
25 148 156 219 658 2,220 2,250 962 503 473 403 310 176
26 148 153 220 693 2,330 2,200 932 497 472 401 303 172
27 148 151 226 730 2,340 2,150 904 487 463 399 296 169
28 149 150 232 760 2,340 2,080 896 488 455 397 289 168
29 149 159 238 789 2,360 2,040 864 482 450 393 283 167
30 150   243 828 2,370 1,990 829 482 443 392 277 166
31 149   252   2,390   800 484   391   165