Aug 26 (Reuters) -Spot basis bids for soybeans and corn shipped by barge to the U.S. Gulf Coast were mostly steady on Monday, amid ongoing concerns about low river levels and as corn futures slumped to new multi-year lows.

* Chicago Board of Trade (CBOT) most-active corn futures Cv1 fell to the lowest levels since 2020 on Monday as expectations of a bumper corn crop and a continued stream of farmer selling weighed on futures, analysts said.

* A closely followed U.S. crop tour run by advisory service ProFarmer projected record crop yields in major producing states Illinois and Iowa, reinforcing a global oversupply picture.

* While the chance of rainfall across the Midwest this week increased, some weather models are calling for a warmer and drier outlook across the central U.S. in early September, forecaster Maxar said.

* That is raising some concerns among traders about low water levels on the Mississippi River slowing barge shipments of export-bound crops and adding logistical challenges to grain movement.

* Fleet delays and falling water levels could further drive up empty barge freight rates, which are already high, brokers said. BG/US

* CIF Gulf corn barges loaded in August were steady at 72 cents over Chicago Board of Trade September corn CU24 futures. September corn barges were also steady at 86 cents over futures.

* FOB Gulf September corn export premiums were steady at about 95 cents over CBOT September futures, while October export premiums also steady at about 100 cents over CBOT December futures CZ24.

* CIF Gulf soybean barges loaded in August were steady at about 68 cents over CBOT November soybean SX24 futures, while September soybean barge bids were up 2 cents at 70 cents over futures.

* FOB soy export premiums for early September loading at the Gulf remained around 110 cents over November futures. Last-half September shipments were steady at about 95 cents over futures.

Reporting by P.J. Huffstutter; Editing by Mohammed Safi Shamsi

For displays of CIF basis, click on the codes in brackets: U.S. CIF Gulf soybeans GRYM U.S. CIF Gulf corn GRYN U.S. CIF Gulf SRW wheat GRYO U.S. CIF Gulf HRW wheat GRYP
For displays of FOB basis, please click on the following codes in brackets: U.S. FOB Gulf corn GRZC U.S. FOB Gulf soybeans GRZD U.S. FOB Gulf SRW wheat GRZE U.S. FOB Gulf HRW wheat GRZF LINKS Corn prices page: cpurl://apps.cp./cms/?pageid=corn-cash-market
Wheat prices page: cpurl://apps.cp./cms/?pageid=wheat-cash-market
U.S. barge freight BG/US
U.S. export sales estimates USDA/EST
U.S. grain export summary GRA/U
Brazil soybean export prices SYBS
Brazil corn export prices SYBX
Argentina grain prices GRA/ARG
Russia grain prices GRA/RU